Outside parts are what mechanics refer to when they talk about parts supplied by a customer and are one of the most common questions a mechanic will deal with in a week. Overwhelmingly though, mechanics will not fit parts supplied by customers due to a number of reasons, both legally and on the basis of convenience.
While many customers think that supplying their own parts is a good way to save some money on a repair, for a mechanic, these parts represent an unknown danger. With the advent of eBay, Amazon and other online platforms it is difficult to guarantee the quality of the part supplied. In addition to this, many sellers have found a way to replicate a genuine part in looks, while not maintaining OEM quality.
These parts are the first reason many mechanics will say 'no' to outside parts, as they are not sure of the quality. As a mechanic, fitting a part that puts the owner of the vehicle in danger is a horrible situation and can even lead to legal ramifications. On top of that, being unable to assure the quality of parts fitted can open up a mechanic to many issues if that part fails, or even if the part damages other systems in the car. For example, if a mechanic fits a customer supplied power steering pump that fails and damages the power steering rack.
Another reason many mechanics refuse to fit outside parts is due to lost time. As mechanics tend to have many years of experience in ordering and finding the correct part for a vehicle, having a part supplied by a customer can be a large cause of lost time if the part isn’t right for the vehicle. The time lost in getting to that point often leaves mechanic with either a disassembled vehicle stuck in the workshop while they search for the right part, or unable to charge the customer for any of the time spent, a loss of hours or days of their time.
Overall, many mechanics are able to supply the parts at the same price or better than what a customer can buy them for over the counter and it ensures you’re buying the right part for your vehicle instead of being stuck with something bought off eBay.