When a buyer returns an item, the Amazon FBA team is supposed to check it for some kind of condition. If it's deemed re-sellable, it goes back into inventory. However, I noticed that 90% of the items were not in re-sellable condition, 50% of the items were sold as used, and 40% of the items were deemed unsellable and destroyed. I was skeptical, so I asked Amazon to send the unsellable items back to my warehouse, but when I opened up the items that were sent back to me, most of the items were in perfect condition with no signs of use!
Frequently nobody checks returns. Damaged and used items get sent back out as "like new" and perfectly fine items get destroyed. Any part of your business that you let Amazon handle will be messy..