[Brent Deines]

If you go to the doctor you sign a waiver, if you go to your mechanic you sign an authorization that often contains a waiver, if you go to an attorney you sign a waiver, if you go to a CPA you will likely sign a waiver. I don't think it is unprofessional, but I do find it annoying.

I had a waiver printed on my invoice, and after I broke my first windshield I had people sign it before I started to work on their car, but after a few weeks my confidence was back and I didn't usually bother any more. It's a good idea, especially if you don't plan to offer to pay for a windshield if it breaks when you are working on it. If you are going to pay for any windshield you break it is not nearly as important.

I agree with SGT though, reading a waiver helps set customer expectations.