You might find it hard to reverse charges. Credit card companies will absolutely reverse fraudulent charges. However, they don't like to get in the middle of price disputes in my experience. If you say you agreed to pay $10, but that you were charged $20, the credit card company may tell you to work it out with the merchant.
It really depends on the card. As mentioned, Amex and Discover really seem to be the best. I've only disputed a handful of times, and each time they refund the money immediately while they figure out who was right.
