In addition to checking our Ratings Tables to see how shops were rated by their customers, judging how well shops communicate, and certifications, ask about the source of any parts that will be used.

Shops can use new original equipment manufacturer (OEM) parts, aftermarket parts from independent parts manufacturers, or used parts. OEM parts are usually the most expensive option, which is why insurers often push shops to use less expensive aftermarket or used parts.

There is some concern over the quality of non-OEM aftermarket parts. For many years, aftermarket parts from many manufacturers often didn’t fit correctly. Some were already rusting when they arrived at the shop, and often they developed rust holes within a year of use.

In recent years, the quality of many aftermarket parts has improved, and in some cases these parts serve as acceptable substitutes for OEM parts. These improvements are in large part due to the establishment by auto insurers of the Certified Automotive Parts Association (CAPA), an independent testing organization. Manufacturers can seek CAPA certification for individual parts by submitting them to CAPA for testing; if a part meets CAPA standards, it will bear a CAPA-certified label indicating that it is of comparable—or superior—quality to its OEM counterpart. Unfortunately, less than one-fourth of parts produced by aftermarket parts manufacturers are CAPA-certified, and quality varies considerably among the non-certified parts.

Most body shop owners told us that the pros and cons of aftermarket parts have not changed much in recent years. They generally prefer OEM parts, and complain that many aftermarket parts are made of lighter-weight metal, have surfaces improperly prepared to ensure paint adherence, and fit poorly, among other problems. In many cases, the shop can make adjustments to correct unsatisfactory parts and absorb the labor costs of the extra work. Good shops simply reject any parts that are not acceptable. One shop owner told us he rejects about 20 percent of the aftermarket sheet metal (fender, hood, etc.) parts he receives, either because of defects or poor fit, compared to rejecting less than five percent of OEM parts.

While shop owners seldom have difficulty returning ill-fitting parts and getting insurers to then pay for OEM parts, such problems can delay repairs. Sometimes the poor fit is not discovered until after considerable work has been done—for example, after a fender has been mounted and a headlight doesn’t fit properly.

Used parts usually aren’t a problem, as long as they fit well and aren’t rusted or dented; if you are paying for repairs yourself and a used part will save you considerable money, there’s no reason not to accept it.

Massachusetts law requires shop estimates to disclose which parts are aftermarket or used parts. If aftermarket or used parts are to be used, ask for a written guarantee for the part—and the labor to install a replacement—if the part proves to be defective during the life of the car. If aftermarket parts are to be used, insist that your body shop (and the insurance company, if applicable) use CAPA-certified parts.