What did you want to tip? 10%? 15%? Let's say it was 10% on $52 vs. the lowest amount available on the screen (18%). We're talking $9.36 vs. $5.20. Were you really $4 less satisfied with his service that it mattered to you? I guess, based on your post, you were. I just think you were a little short-sighted.

Had you asked if there was a way to customize the tip, that might have helped. If he said "no", I would have said "okay, I'm going to put zero on the credit card charge and I'll just give you a cash tip" and then given him the $5 or whatever you wanted to give him once I was out of the car and on the curb WITH all of my belongings.

As someone else wrote, "when in Rome...".