If everyone had to write something too about there experience, this would mean that everyone else could decide how they would personally rate the service.

EG:

Details of work, Price, How easy to talk to, sticks to price estimates as workably possible etc etc.

The everyone could write what happened

EG.

He did work without telling me/didnt do work he promised and still charged it, scratched paint etc whilst in his garage. Got seats dirty, left a wheel nut loose, or more serious stuff like forgot to connect a hose properly which resulted in blown head gasket. That sort of thing which means each person can decide how bad in their opinion the workman/garage was.

I think a rating service is a good idea, especially for people who have moved to a new area and don't know any poeple to ask etc.