The first thing you'll want to do is find out if your auto-mechanic is certified to be doing auto repair and maintenance work in the first place. Look around the waiting room for neat certifications from reputable sources hanging on the wall and in most cases your auto-mechanic will check out. If you don't see any certifications upfront, it is your responsibility to ask what certifications and qualifications your auto-mechanic has. Otherwise, it's beyond a probable doubt that you might end up paying way more than you have to for a service of lesser quality.
There is no test you can do on your own to determine whether or not your auto-mechanic is offering you a good service at an equitable price. That's why one needs to seek out people who have dealt with the auto-mechanic before. That means getting referrals. One can simply go online and search the name of the auto-mechanic and read any comments that are attributed to them. Of course, you'll know what to do then; a good mechanic is five, four, even three stars while a bad mechanic is two or one star. Read every comment with a grain of salt though, not every person writing an opinion on the internet is necessarily speaking from sound logic and experience.