If it's not fit for purpose then you shouldn't have to pay return postage.
I hear you on the lack of confidence though. I'll buy any old crap online but I much prefer to handle guns and stuff in the flesh so to speak. Unless there's a crap ton of money to be saved buying off t'web then I'd rather be able to look the guy in the eye and say "hang on, this thing feckin rattles, get me another".