If their wages are low, I'm generally cool with adding to them, as the minimum an many lower wages haven't gone up in 20 years. Pretty much any job with that long term custom I have no problem. I haven't been asked or heard of tipping my auto mechanic. My garage charges around 200 an hour so that's a no. They are a great shop for Porsche (classic) and give a lot of things for free but I know those guys make enough per hour.