Three words no shop manager ever wants to hear are customer supplied parts. There are some really good reasons for that, and it’s understandable why many shops take a “just say no” position on the practice. But there are also plenty of perfectly reasonable arguments why—at least under certain conditions—it might be okay to say yes once in a while.

Your willingness to install parts that a customer just handed you likely depends a lot on what type of shop you run. Having previously managed a dealer service department, a custom/ performance shop, and a restoration business, I’ve dealt with such requests at each operation. And in all three businesses, I have both accepted and refused to install various customers’ components.

Dealerships almost universally refuse to put parts on a car if they didn’t sell them. In order to maintain warranty coverage (and to avoid compromising their franchise agreement) they’re obligated to use factory parts in most cases.

For indie repair shops, survival relies on throughput in the service bays. Most have a network of wholesale suppliers at their beck and call who offer parts from numerous manufacturers. The vast majority of common repair and maintenance parts can be ordered, delivered to the shop, and installed the same day without the vehicle ever having to leave the bay. These shops can’t afford downtime while their customers go shopping around for parts.

Custom shops, including restoration and performance businesses, probably field the most requests to install customer-sourced parts. They’re used to dealing with out-of-the-ordinary requests, and the nature of their projects means they may not even have a source for what a customer is looking for. Time also tends to be less of a factor for these shops, and for all these reasons, they’ll likely be the most willing to work with their customers in this way.

Understanding Customer Motivations

Although most vehicle owners wouldn’t give a second thought to sourcing their own parts, it’s important to understand why some absolutely do. It most cases it can be probably summed up in a single word: control.

Because modern cars are complex and represent a huge investment for most people, trusting the people who repair them is a huge factor. Whether it’s managing the overall cost of a given service operation or simply ensuring that ‘the right stuff’ is going into their car, a certain percentage of vehicle owners will always want a say in how their cars are serviced. Educated customers often know what they want, down to a preferred brand, and if a shop can’t guarantee them that brand, they may just prefer to hand it to them.

While shops have always had to deal with the nickel-and-dimers and the know-it-alls, the reality is today’s information economy provides the general public more information than ever to advocate for how their dollars are spent. Online communities reliably pool tribal knowledge to influence which products (and shops, for that matter) are trusted and which should be avoided at all costs. A few minutes searching a handful of online retailers can save owners huge money for the very same parts their shop is offering. Video tutorials arm capable owners with enough information to at least have a reasonable conversation with a service adviser.

Beyond mere cost and quality concerns, we can’t overlook the DIYer. A lot of people still see performing their own basic maintenance as a point of pride and virtue. Despite their best intentions, many old-school DIYers simply run out of skill when it comes to more complex repairs on modern vehicles. They may have already purchased parts with the best of intentions for a good Sunday afternoon under the hood, only to discover they’re in over their heads before they crack the first beer.

And let’s not forget, aftermarket performance upgrades and custom accessories are huge business. Even shops that don’t actively peddle aftermarket goods may have enthusiast customers in search of upgrades, and those owners will still want to work with a trusted shop to do the work they’re not able to do themselves. Saying yes to that custom exhaust install could result in add-on labor for other services while the vehicle’s on the lift.

Why Say No?

The reasons for refusing to install customer-supplied parts are good and plenty. The most common reason you might refuse seems obvious: you make money on parts sales, so why give up a significant part of your revenue stream? Bolstering the bottom line on each sale is undeniably a factor, even if the margin on labor is typically 2-3 times that made on parts, there are important operational considerations that also drive this decision.

The biggest one may be getting a proper diagnosis of a vehicle’s problem before parts are ever ordered. Allowing a customer to simply walk in with parts for you to install assumes they know what the problem is in the first place. Fixing a symptom is not necessarily the same as eliminating the cause of a problem, and customers tend to get defensive when you tell them the repair requires more work than they anticipated.

Following that line of thought to the next step, how do you know the customer has brought you the right part? Or for that matter, all the parts required to actually make the repair? Professionals know from experience that you almost always need more to make a repair than just a single part.

Finally, is the part that the customer brought you even worth installing? The proliferation of cheap, unbranded parts coming from unknown sources today means a lot of stuff you can buy from eBay, Amazon, and other online sellers is simply junk. It might look like the right part, but there’s no guarantee it will fit correctly or perform reliably, to say nothing of how the seller will deal with a warranty issue should there be a problem.

Why Say Yes?

Because not all customers are created equal, there are some good reasons your shop may want to install the parts a customer hands you. And most of them are a matter of trust and rapport with certain owner types. It would be arrogant to assume that no owner is smart enough to know what their car needs.

Well-informed enthusiast customers may know their cars as well as you do and in fact may be your best advocates if you’re willing to work with them. They’ll appreciate your respect for their knowledge and flexibility to accommodate them. Hell, they may even do some of the hard work for you when it comes to complicated diagnoses, researching problems on their own time.

There are a couple of very real benefits, especially for smaller shops, to letting customers bring you their own parts. First, it means no lost time for your parts or service manager looking online or calling around to find out who has the part and when it can be here. Your people can focus on other jobs. Second, it doesn’t tie up any of your working capital. The parts come in pre-paid, ready to install. One less check for you to write, one less delivery driver to wait for.

At the end of the day, your primary objective is to sell labor hours to happy customers. That may occasionally mean installing a part you didn’t sell in the interest of building trust and a more substantial relationship with some customers.

Navigating the Middle Ground

Should you choose to say yes to the odd special request, proceed with reasonable caution to protect yourself. At the very least, reinforce with the customer that you’re making a special accommodation on their behalf. If a full diagnosis is required before starting a repair, don’t feel bad about charging realistic diagnostic or inspection time to confirm the need for repair before using their parts.

If all is good up to this point, get the customer’s written consent to install the parts they provided, including a thorough accounting of their exact provisions with manufacturer names, part numbers, and quantities. Have them sign off that you cannot and will not be held responsible for the accuracy, completeness, or quality of the parts provided.

Since you’re making a special exception for their work, you may want to consider charging differently, especially if they’re bringing you parts you already sell. Just as some fine restaurants will allow you to bring your own wine to their table (albeit for a small ‘corkage’ fee), you may choose either a different labor rate for customer-supplied parts or perhaps billing on a time-and-materials basis instead of flat rate, especially if you can’t count on the parts you’ve been handed.

Finally, make sure the customer understands that any warranty by the manufacturer is for the component(s) only and that any labor required to replace a warranty part will be the customer’s full responsibility. You are under no obligation to perform warranty labor on a failed part you didn’t sell in the first place.

If you’re still not comfortable with what’s being asked of you, don’t forget it’s your shop. You can always play your Nancy Reagan card and just say no.