I'm a very small seller, 50-100 books per month. My On-time delivery rate has fallen below the required 90% and I received a warning today. I checked the sales that dropped my metric, and every one came from the same buyer over a span of separate orders. It appears that, for whatever reason, the package (I sell books exclusively) is held at a USPS regional distribution facility for about a week every time.

I already use Automated-handling time because I ship within 1 day regardless, and I buy shipping on Amazon, but I do not use shipping setting automation (SSA) given I've read it often requires you to use a faster (more costly) shipping method.

The buyer seems to be a drop-shipper or something like that -- not sure -- but they've purchased a number of books from me over the past year or two, always with a different name going to the same address, and occasionally Amazon won't let me use the bound printed matter / media mail rate from "buy shipping", which makes me think their algorithm knows there is an issue there already.

I don't have any other late deliveries -- just to this single entity. Should I cancel future orders from them (if this is even an option)? Should I use a faster ship method to them specifically? Is it possible they have a deal with the local distribution center to hold packages for them (I assume they order a huge number of used books off of Amazon on a daily basis) and that increased speed wouldn't help? Just not sure how to proceed given I don't want to mess with the protection that SSA provides. I think I did it one time in the past and they were always wanting me to send it express or something like that, which is obviously untenable. If I'm mistaken on SSA (shipping settings automation), please inform me otherwise :) . Thanks