Does Amazon cherry pick customers, or do they get as many returns as we do?

SUPPORT, can Amazon give the Buy Box "Feature Offer" to third-party FBA sellers when it believes the buyer is likely to return the item (instead of listing Amazon's item in Buy Box)?

We sell one name brand's items via FBA that Amazon also sells.

Our FBA return rate is nearly 15%, while Amazon shows their return threshold is 8.7%. Large discrepancy!

I suspect that Amazon gives the Buy Box to third-party FBA sellers when it believes the buyer is likely to return the item.

In addition, we get charged for returns when the buyer claims the item is "too big" even though the item dimensions are clearly stated in the listing, even in the title.

The cost of returns is killing us and seems strangely high.

We hardly ever get a return for an actual item issue (if anyone would look), like damage, missing parts, or actually not-as-described.