Agreed that it happens, I've been offered same every year ( this is my 22nd in a row). BUT almost always I haven't been serious about the offer and actually pulled out cash...then see what happens on the spot. I've also had the opposite happen in that companies would not do a transaction on the floor even when I was ready. I've had to meet someone in a coffee shop outside of the convention centre to give a deposit cheque. Believe me it was not convenient for me

So it depends on the company and if they will respect the rules of the game or not. Try to actually buy a bass with cash on the floor....many will, many won't. I've had the rule quoted to me. They don't check what goes out? They sure do, maybe not everything but most items not able to conceal in a small bag. In fact, someone from the exhibitor booth with that exhibitor badge usually has to escort you to the exit to get it through security. But my point is that it shouldn't be taken for granted that you can or should be able to buy anything you want like a store to the public.