Installation of customer supplied parts.
There are various reasons why an auto repair shop won't be tempted by the idea of installing customer supplied parts.
Reputation, Profit, Liability, Efficiency, and Warranty
No car component would ever fail in a perfect world, regardless of its origin. Unfortunately, the reality is much more different. Let's say a component is installed and after some time it fails, the customer will have an unpleasant experience with all parties involved. The auto repair shop won't be happy because now the auto technicians have to do the job all over again for free and they have to pay them once more for the same job because they don't work for free. Afterwards, that same customer will share his or her experience with family, friends, online review sites, and social media. Businesses work extremely hard to build their reputations by providing customers with exceptional customer service, so a business won't risk harming its reputation.
Even though this is a sensitive subject, it has to be addressed at all costs. An auto repair shop must make a profit in order to remain in business and provide customers with the latest diagnostic equipment and tools. In addition, the auto repair shop needs profit to provide competitive compensation for its talented technicians and training for the modern complex vehicles.
For the majority of auto repair shops, nearly 50% of their revenue comes from the gross profit generated by the sale of parts. They cannot cover their expenses with just labor.
If an auto repair shop agrees on installing a customer supplied part, they are accepting the liability no matter whether the failure is caused by improper installation of that same part or the part itself.
Because of the disputative nature of our present society, this becomes a serious risk for the business. The auto repair shop cannot print any waivers in order to make customers sign on the repair order that will eventually limit the exposure to the business itself. The fact of the matter is that typing a disclaimer on a repair order in its very nature is an admittance that they are aware of the higher risk of failure. The customer may have bought the part online, from a new car dealer or a parts warehouse, this does not matter at all before the court. In their eyes, the repair shop technician/mechanic is the professional, who was the last one to put their hands on the car component. He or she should have known whether the part wasn't of good quality or that the part was bound to fail after a short period of time.
Each part is a perfect fit in a perfect world. If the customer has to have the car back that day but the parts supplier the customer bought the part from can’t deliver the part until the next day, who is going to pay the labor for the technician for taking it apart and putting it back together even though no new part was installed?
The finger pointing starts when the repair shop installs a part they did not supply and that very same part fails. On one hand, the shop will say that the part is defective and on the other hand the parts warehouse will state that the part was improperly installed, regardless of how simple the job was. At this point, the customer is stuck in the middle because the parts warehouse doesn’t want to pay for the labor for the shop to redo the job and the shop doesn’t want to do the job again for free (although they are required by law to do so as stated above). The parts warehouse only sold the part and will only replace the defective part.