The main issues you get are when returns are put back into stock but haven’t been sufficiently checked.
I used to work for an online retailer who sold things like games consoles and the amount of return scams we got was absolutely shocking. If you sold a games console with a free game (usually a code inside the console) people would take the game code out, or copy it, and then return the console and have the game. Other times they would take an iPad out, put a brick in the box and then shrink wrap it. Or buy counterfeit AirPod pro’s and swap them for the real ones and return the fakes.
The problem is compounded because people want to buy “new” items with shrink wrap around them, so it’s harder to check returns aren’t scams when the scammers have shrink-wrap machines.