If I’m not mistaken, there are laws prohibiting a vendor from selling a product for more than it is advertised in the store. For example, if they have a menu item listed for $15 on the menu, but then tell you after you’ve eaten it that your bill is now $20 (apart from tax), that is illegal. I know that’s the case in NYC where I personally encountered that problem on the vendor’s side (at a cafe there was an item with an incorrect price tag sticker attached, and by law I had to sell it for that amount). It might be another angle to take to fight these bogus charges. I think you could easily argue that the surcharge is nothing more than a hidden part of the total price of the purchase which they don’t inform you until after you’ve already transacted.