Never. Usually they ask why I'm returning it, and I just decide how literally true I want my answer to be, and that's that. I try to return it before the deadline, though, and I ask what the terms are at the time of purchase. Sometimes stores will let you return stuff later than the deadline, anyway.
In that case how is it "abuse"? Are you speaking of your intent?
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.