If we want to live in a society where we have 14 days to return a product bought at a distance for any reason, then we need to accept we live in a society where we run the risk of receiving someone else's return. Saying people "abuse" the system is subjective, and there's no clear evidence of that in this case.
Personally, I have returned items in the past (GPU due to coil whine etc) and I've also received items that I suspect have been previous returns as they are opened, but as the items have been functioning perfectly I've seen no reason to send them back.
What do people expect?
If its used or a return it should be marked as such, and most likely priced as such.