It might not always be 'poor fit'. My wife buys multiple items, keeps the one she wants, and has me return the others. A cashier inevitably checks 'wrong fit' on the 'reason' area of the return form, even though they probably fit just fine. They didn't 'fit' my wife's mood, perhaps, but certainly would've fit her body just fine.
I've found myself doing this more frequently. Basic reasoning is that unless I'm at some store that is far outside my normal commuting path, I'd rather spend 20 minutes just grabbing things that look roughly right. Then I can try them on at my convenience and return what I don't like sometime over the next week or two.
This saves me time in the store and also makes the decision less agonizing since I can make it over a few days.
So, yeah, you're probably dead on about how 'wrong fit' can be interpreted.
