Despite your "warning" I'm sure there will still be tons of people trying to do these things, and then calling for the manager and then threatening to call HQ, etc... Some people agree with your stance, others feel it's OK to do the return/rebuy thing. It's all part of the tradition of BF :)
Seriously, stores could avoid so much of this with a clear policy either posted throughout the store a few days before BF, printed on receipts, etc... then it's written in black and white and there should be little room for argument at the store.