Oh you got hit with one of those , I haven’t had one for years! You will win IF the customer isn’t that bright. Depending on what the ACTUAL weight is of package returned , usually the rocks weigh more then the item shipping / product weight . Go to UPS website and create a help ticket or contact them and have them email you the weight of the package when it was processed through their facility. They weigh / measure it to to see if they need to charge you more for package. Usually this weight is more and then you have proof that they sent you the rocks. If the customer is actually a good scammer, then they would of sent back the same weight of original package, then it is she/he said . You will lose since you could of put the rocks in it and then get refunded AND keep product. So you would be scamming Amazon in their eyes!
Gotta love the Human Race!

Everyone reading this do not do this scam as mentioned above the correct way . We need to use Morals in our Society , which is lacking.

Like @JustSelling said, you need to have evidence. Without evidence, the customer can say you are scamming them.

Contact UPS. Open a case. But know that you have to refund at least 50% within 48 hours of receipt or else Amazon will refund in full.

What about how Amazon auto-applies a refund if the seller does not do so within 7 days. The safe-t claim says it takes 10 days to respond.

I have not had the direct experience, but if this was an auto-approved 3rd party pro seller return, amazon may auto-refund within 24 (48?) hours of the return showing received. There are threads by sellers issuing $1 refunds and such to avoid the auto-refund taking the full balance.

Not sure exactly how all that works given my category (handmade) is not subject to auto-approvals, but strongly recommend you research it immediately and take any action that circumvents a full automatic refund.

File an IC3 crime report and a usps fraud report. Provide this evidence to amazon along with the weight.

I am just so sorry… I completely feel your pain… geeze… that is awful.

Step 1. Take picture of everything you received.
Step 2. File a case with Seller Support to report the buyer with mail fraud.
Step 3. Report mail fraud to USPS Inspector General.
Step 4. Write to the buyer telling him he committed mail fraud.
Step 5. Wait for A-Z claim.
Step 6. Represent your case with A-Z claim.
Step 7. After A-Z debit your account for refund, file Safe-T claim, with all the information you have.
Step 8. Wait for reimbursement.

Amazon gives you 48 hours from (tracking showing) delivery to issue a refund. You should refund at least a nominal amount (like $1) to prevent Amazon from auto-refunding the customer in full. Follow what the other posters stated by getting the shipping weight from UPS so you can prove that you did receive rocks from the buyer. Then wait and see what your safe t claim answers.

Those people refunding $1 eventually got the entire amount refunding from them I would not try it if I were you. It only bought them a small amount of time- and then the auto refund bots detected the quote-“error” and refunded the entire amount. You could lose everything if you dont refund 50%.

I might try contacting the buyer and say, I received a package from you today thinking it was your return however it just had rocks inside, I want to double check with you first and make sure the package wasn’t sent by mistake and possibly mixed up with your actual return. Otherwise I will have to file a claim with UPS for mail fraud- this is punishable by fine and or up to 20 years in prison.

Might make them think twice!