In the case of cab drivers, it really isn't a matter of negotiating for volume--they might pay 5-6% effective rate, but I bet that their payment processing provider isn't payment more than 1-2% for VI/MC (since they aggregate all the cab volume). The rest is the cut taken by the guys that had to develop and install that video screen / credit card machine--including paying for its online connectivity (GSM), etc. So there are legitimate costs, as well as profit to be made there

I think the real reason cabbies hate is the regulatory requirement to take credit has forced them to sign up with those ad screen / payment companies in the first place. OTOH, as a cab rider, I definitely like paying by credit card--for one thing, it makes the hand-written "receipt" so much less necessary for expense report purposes