Meh. It may be illegal, but it's one of those technical violations where the motivation really matters.

A cab driver using a much cheaper service vs. the rent-seeking credit card processing they are mandated by law to use? That's a morally correct action. The immoral action (imo) is to continue to feed into the fraud that you yourself identified earlier in the thread.

I have very little problem with a cab driver doing this, just as I have very little problem with you reporting it for the reasons you mention.

And having a rather interesting early start to my career - I assure you "native" citizens get away with this kind of crap all the time.