Oh, well it definitely is, at least in the US. They’re not getting paid below minimum like waiters are, but tipping is still customary. Normally it’s only the ones with the towels on the other end getting tipped, though. I always assumed that they all split the tips equally, but I guess I don’t know.

If I were taking a car there knowing it needed extra work on the front end, I definitely would bring tips for both ends.