How to choose a suitable car mechanic?

ask your wife, she has slept around with a few.

Driving trial You and you mechanic.

Find problem.....

I usually recommend asking around friends, family, co-workers, etc. if they know of anyone reasonable and reliable.

If you don't have anyone you can ask, then check out shops online - read reviews, etc.

In my experience 99%of so called mechanics are conmen so find one who is generally busy and find someone who knows him well. 

Find Out Who Services the Big Business Fleets in Your Area. ...

Search for a Good Mechanic Online. ...

Choose Someone From the AAA-Approved Auto Repair Network. ...

Look Up ASE and Manufacturer-Certified Shops. ...

Check With the Better Business Bureau.

Aside from the other good advice here, maybe look for a local shop that is obviously busy.  

Ask several of your friends and family to see if they can recommend anyone.

Search using google, look at the google reviews, and yelp reviews.

Suitable for what? You didn't say.

Ask your friends who they use.