I sell a ton of shoes on AZ via FBA.Protip - be very careful with Apple Watches. If the customer returns it, they often fail to remove it from their iTunes / iCloud profile, and often won't respond to your messages to do so. That leaves you with a watch you can't resell since it's locked to their account. I've had at least $2500 in such returns this year - which has been a helluva hit to my bottom line, as those are losses I simply can't recoup.
The upside is excellent ROI.
The biggest downside is high return rates. Every so often someone packs up a filthy old pair of sneakers as a return and keeps the nice new ones I sold them.
I have 100% success being reimbursed by Amazon when someone returns unsaleable goods.
When you do a removal order on an FBA item and it comes back in unsaleable condition, you file a claim in Seller Central, sending in pix of the removal order shipping label, removal order packing slip and pix of the item itself.
I don't sell Apple watches anymore, but I would suggest taking a photo of each box including the serial number alongside the FBA box label or FBM shipping label before sealing up the box. I was 100% reimbursed for a watch that didn't match the one I sent out, which I was then able to sell as 'Used - Like New' for 90% of the New price.