I could be completely wrong, but I've read various mass-media articles that suggest that a single stolen credit card is only worth $1-3 on the black market. If

I could be completely wrong, but I've read various mass-media articles that suggest that a single stolen credit card is only worth $1-3 on the black market. If that's true, unless the dude with a Square reader is planning on using the stolen credit card number himself (which is a surefire way get caught), the twenty bucks this hypothetical fraudster legitimately charged you far outweighs the profits he'd get from selling your credit card data.