Actually, most repair shops are honest.
Incompetent mechanics end up throwing parts at a vehicle until the problem goes away.
Unfortunately, the customer almost always ends up paying for this. A referral is one of the best methods of finding a good repair shop. So, perhaps you are new in town and have no one to ask. I have found the next best thing is to check with the auto parts stores in your area. They have generally heard about the honest and reputable shops in the area.