Be vary of garages providing estimates on the phone without seeing your vehicle first. Estimates mean little without knowing the detail of the problem.
Get a referral from a good friend who has established a working history with a good garage.
Stick with one garage if possible so they will know your vehicle's history, saving time and money when diagnosing the problems.
Find a shop that calls you before any work is done, and then shows you the parts replaced while repairing your vehicle.
You may with to take the mechanic for a test drive to point out the problem before they begin any repairs.