There are actually 3 ways that I know of that these sellers are doing this:

1. What you said: parent-child relationships.
   However, this is done by more amateur sellers. Only requirement is that firstly, item has been out of stock (permanently) and secondly, to change the brand. Only the brand needs to be changed, not all listing details need to be changed. It’s easier to do and easier for Amazon reps to see the violation, as compared to the other methods. When variations are done, the variations names will appear on top of each customer review. It’s not variations (aka parent-child relationships) if there is no variations names above the reviews.
2. Co-opting a listing and selling in that listing.
   So basically the seller changed ALL the listing details to sell their product. Hence ASIN A will be changed from productA to productB and seller will still be selling on ASIN A. Seller may also co-opt other listings and either create variations with the other listings or merge as “duplicates”. This does provide some level of blockage against detection because many reps don’t even look at the reviews section when they see a case you created about this. They will simply be like it’s your words against the other seller’s words about what the product details should be. Provide proof that you are right.
3. The most experienced sellers do this. Create a new listing for the product they want to sell. Co-opt other product listings to this product (basically change all details to this new product). Then merge to their new listing as duplicates. Hence they are selling on the actual product ASIN they created while benefiting from reviews of the other ASINs.
   This allows them to “recycle” successfully co-opted listings of other products. More on this towards the end of the post.
   This method makes it so the more incompetent reps at seller support will not be able to understand what is going on with reviews of other products. Why? The actual ASIN you can see in your address bar is the one the seller created to sell. The other ASINs of other products are not visible, even in search. They have basically been “deleted” when merged this way. Firstly, most reps are familiar with this happening with variations. They are confused when they don’t see variations and see that this ASIN you reported has been selling this product all along, they don’t know what to do, simply try to close case without resolution to move on to the next case they can actually resolve and keep their performance metrics up. Case resolution is that it has been transferred to another team, so this case appears closed. Lies - they don’t know what’s wrong and what team to transfer to. Secondly, remember the “other ASINs” of other products had all their product details changed to this product the seller is selling. So even if you instruct the rep to look at the ASINs merged with the one you are reporting, many of them will see the ASINs are the “same product”, hence “properly merged”. I had a rep on the phone who was this incompetent - I soon realized it’s best I hang up and try again. Thirdly, it seems these sellers try to make little small changes to the listing at a time using several accounts - in order to have a super long change history that will potential make it more difficult for Amazon reps to figure out what’s happening. I was on the phone with a rep for a long time who was telling me how much of the change history he had to load through to be able to find what the original listing was.

Some information I have gathered:
1. These seller accounts that you will find in your search are likely not the ones being used to commit violations.
I have explained this in one or more of the threads linked in the OP’s original post. The more experienced sellers who have been able to do this for a long time likely have several seller accounts.
a) They have “disposable” seller accounts. These accounts do not have any monetary value to the seller, they do not make any sales, they are easily replaceable. They are only used to commit these violations - in case Amazon catches the violation, this account gets taken down, the actual account making sales remains protected. You will not find these “disposable” accounts listing the product for sale at buy-box price.
b) They may have several “monetary” accounts. There may be a few reasons for this. Firstly, it may be because of the low quality products that they sell will have high return rates. High return rates causes Amazon to automatically remove the offer from the particular seller. It can take a couple days to reinstate the offer (after sending a plan of action). Hence when that happens, the other monetary account gets the buy-box and the seller doesn’t lose out on a couple days’ sales. Secondly, for “lightning deals” sales. For lightning deals, Amazon does not allow sellers to price a certain percentage higher that the lowest offer over the past few months. Hence with some of the accounts, they offer a price higher than their “normal” price, but then use those high price offers to still price high enough during a lightning deal. The high-scale “monetary” accounts will usually list the product with FBA.
c) They may have a “scout” account or two. These accounts will basically scout for those listings that are out of stock. Then the scout account will list an offer for those listings. This will usually be a super high-priced offer so that they don’t get the buy-box and also so buyers do not buy from them (since they do have actually have the product in case someone buys from them). They do this to kind of “reserve” the listing for their use. So other sellers who are looking for out of stock listings will not see these “reserved” listings since it’s basically not of out stock anymore. You may see these accounts still with an offer on the listing (since their offer gets transferred over when a merge is done) unless they then changed their inventory count to 0. The reason also for these scout accounts instead of just using the “disposable” accounts for this purpose is firstly, to keep a record of the listings they can use, since the “disposable” accounts will lose all access to the list of listings to be used, and secondly, to keep an offer up on the listings (keep them “reserved”) in case the disposable accounts get taken down. The scout accounts usually do not commit violations.
2. The listings that these sellers have successfully co-opted are often recycled.
The reason these sellers first create a new listing and then merge other listings with the new listing (method #3 of hijacking) is so they can recycle the hijacked listings. Often times these sellers are selling low quality products with a high rate of negative reviews. Usually 1-3 stars if they didn’t do the hijacking. Ofcourse, the aim of the hijacking is to keep reviews around 4.5 to get lots of sales. However, as they sell, real actual reviews of the product start flowing in and after months of selling, their overall ratings reach 4.0 stars or lower. They usually will merge more listings with the product to boost the ratings up. However, the number co-opted listings they have is limited, and they are likely selling lots of products where they need to use such co-opted listings of other products. At a certain point, the ASIN they created by itself has accumulated 100’s of 1-3 stars ratings and it makes better sense to them to abandon the ASIN. Remember the reviews of 1-3 stars are tied to that one ASIN, so they can just abandon it. So what they do is they unmerge the ASINs they had merged. The ASINs they had co-opted of other products will retain their high reviews and ratings. They abandon/close the listing they had previously created (which now has 1-3 stars rating), they create a new listing of the same product, do the merge again and once again start at 4.5 ratings. And keep recycling again and again. If they had simply co-opted ASIN1 and listing an offer on ASIN1, new reviews would be tied to that ASIN. In this case the reviews are tied to the ASINs they create and abandon so they can reuse the other ASINs that they had hijacked. This also creates a lot of changes in the change history of these co-opted listings that creates a lot of work for Amazon reps to be able to figure things out. Also, usually this recycling is done with the same type of product. Say seller is trying to sell pest repellent. They co-opted listing to pest-repellent, then when they abandoned the listing it was merged with, then unmerge, they will usually change some details in the title and pictures in the co-opted listing, and then merge with the new listing - and they do this recycling many times. This shows Amazon reps that there were changes made to the listing but as far as they can see in their change history, it was pest repellent for the most part.

I am compiling a list of sellers to report who are doing this. You may help if you wish. I need the information in the following format:

Brand1

Sellername1
ASIN1
-brief explanation of what’s being sold, what did the seller do (variation, co-opting or merge as duplicates)
-screenshots of reviews/Q&A of other products
ASIN2
-brief explanation of what’s being sold, what did the seller do (variation, co-opting or merge as duplicates)
-screenshots of reviews/Q&A of other products
ASIN3
-brief explanation of what’s being sold, what did the seller do (variation, co-opting or merge as duplicates)
-screenshots of reviews/Q&A of other products

Sellername2
ASIN1
-brief explanation of what’s being sold, what did the seller do (variation, co-opting or merge as duplicates)
-screenshots of reviews/Q&A of other products
ASIN2
-brief explanation of what’s being sold, what did the seller do (variation, co-opting or merge as duplicates)
-screenshots of reviews/Q&A of other products
ASIN3
-brief explanation of what’s being sold, what did the seller do (variation, co-opting or merge as duplicates)
-screenshots of reviews/Q&A of other products

Let me know if there is a better way to present the information to seller performance.

A lot of the ASINs will have several sellers selling it (usually belonging to the same one seller) although not all of them will have the buy box at a particular time. However they are obviously all in on it. A way to find the ASINs is to go to each of the sellers’ storefront > see products tab. Repeat with each ASIN you find under the tab, ie open ASIN, record it if fraudulent, see sellers selling it, see ASINs being sold by each of those sellers, and repeat. This will give us a HUGE list of ASINs and sellers.

Some other things I’m looking for:

1. If the same brand has the same (group of) sellers listing under ASINs that have been compromised. It will mean that the seller accounts likely belong to the same one seller. It’s too much coincidence to not be the same seller.
2. If there a seller account that is on more than one ASIN that has been compromised, it’s obvious it’s not by accident. These are the seller accounts I am looking for.
3. If the same fraudulent seller account is selling brand1, brand2, it means both brands likely belong to the same seller. Which means that the other brands being sold by seller must also be looked into. If other seller accounts are found selling the other brands, they must also be looked into, it is likely those seller accounts will belong to the same one seller as well.
4. Remember about the ASINs that sellers eventually abandon and create a new one and reuse co-opted listings? Would be great if we presented a list of those abandoned ASINs. These ASINs will have a history of being merged with the same listings that are merged with the ASINs were are reporting. Also, those ASINs most likely will also have a history of being sold by the same sellers were are reporting. To find these ASINs, simply take the ASINs you found above, copy paste the brand, product name in the search bar > change category dropdown to the category the product is in > search > on the left pane scroll down and check show out of stock. If there are other similar products that were being sold by that brand they will show there. I have found such listings many times. You may find many duplicate products (products that are abandoned).
5. Also do the above with the scout accounts. You will see many duplicate products under the scout accounts. These are listings that are in the process of having their details changed.