You're kidding, right?

The guy hands me a bill for 75 bucks an hour labour and I'm going to tip him?

I think not.

Next, my lawyer's going to be wanting a tip.

when I go to a garage, I am paying enough as it is. if they do a good job and i feel they are honest and not trying to get me to pay for something that does not need fixing, i would continue to use their business and recommend them to others. if it is someone who is a backyard mechanic is good and does work on the side i would pay them what they asked and maybe tip them out of appreciation. I am not a well to do person so i try and do what i can do.

So you get mugged in broad day light and you tell the mugger oh by the way I have a C note in my shoe. Who tips a mechanic they have probably cleaned you out any way.

Again, as with plumbers, they probably have more money than you do. Just pay the bill.