yeah, it's not cheating but it's kinda disrespectful.
you *are* getting ripped off, pies are what, $8.00? I am the master of all pies but I wouldn't go giving one to a married man... it's... distasteful. stranger or potential friend. Just like she shouldn't except a car servicing from some new potential acquaintance in exchange for her old designer sheet set. ;) (behind your back, none the less)
tell the woman you thought twice about it and you aren't going to except the pie, and many apologies, thanks so much anyways, hope you're not too disappointed. (she shouldn't mind.)
whoever is telling you to tell the woman you can't because your wife is paranoid... that would just be rude. the reason you can't, is because you respect your wife in a potentially (even if accidentally) disrespectful situation, and don't want to take a chance with that.
in your heart you knew the answer, since you asked in the first place.