First, try to research various aviation certifications. An aviation mechanic will be FAA certified in either airframe or powerplant, but most will be certified in both, commonly known as an “A&P” or Airframe and Powerplant Mechanic.
Another credential to look for is professional affiliation. The Professional Aviation Maintenance Association (PAMA) is an organization that promotes ethical and professional practices in the field of aviation maintenance. PAMA and the SAE Institute provide additional certification that validates the core knowledge of FAA certificated A&P mechanics. Completion of this program certifies a mechanic as an Aviation Maintenance Engineer (AME).
Check out your local shops. This means stopping by and checking out the facilities. You should be looking for key details such as the cleanliness of the grounds and work areas. Take notice of the makes, quantity, and quality of the other customers' aircraft. If you fly a Cessna 172, and the only aircraft you see around are large corporate jets, this may not be the most appropriate shop for you.
Ask around. Your fellow pilots/aircraft owners and the owners or managers of local FBO’s or flying clubs have certainly dealt with getting maintenance done and can probably steer you to a reputable shop. Find out how they feel about their mechanics.
Talk to the mechanic, ask questions and request to see the old parts when they are removed. When mechanics put a face to the aircraft and know that they may be talking with you again, they are likely to be more particular about how they perform the repairs.
NOTE: In addition to signing your aircraft’s logbooks, a reputable mechanic should provide you with a work invoice that lists all repairs, parts, and labor charges that were performed on your aircraft.
According to 14 CFR 43.9(a), a proper maintenance logbook should include:
If the maintenance or work includes a major repair or alteration, the mechanic will be required to complete additional paperwork approving the aircraft for return to service. This includes repairs or modifications that utilize a Supplemental Type Certificate or “STC”.
Helpful Tip: After you find what you believe to be a quality mechanic, but before you dedicate your airplane to that person, test out the relationship you will have with him/her. Take your airplane in for just an oil change to see how you will be treated.
Warning: Be wary of up-selling. If it always seems like major problems are being found every time you take your aircraft in for routine maintenance, you may want to get a second opinion from a different mechanic or shop.