I almost always allow returns, except on things like 20+ year old computer parts. I sell about 100 items a month, and I get maybe 1 return per month. Of those, 90% are because they bought the wrong thing or changed their mind, not because the item was defective. They have to pay shipping both ways unless it was not as described. And if the item shipped "free" they get my actual shipping cost deducted from the refund. It doesn't happen often enough to worry about.
TiVo Mini (v1) x 3
Left DirecTV 4/15/07. Left TWC 8/8/11. Now on Comcast Xfinity.