There aren't any rules, only customary recommendations. The interweb is full of half-truths and bull. That's the point in all this. Not every driver does a job worth a tip and not every rider/guest has a tip on them to reward them either. Those are the breaks and I will never be sorry for it. Again, tip them if you have it and they genuinely deserve it. I certainly never judge either way because it's really a flea on an ant's ass in the game of life.