Should I install customer-supplied parts on a performance or diesel build?
Short answer
Only with full labor rate, a signed waiver, and the customer paying for the parts you'd need to correct a bad or wrong part after you're already into the job. On a build, a customer's cheap online turbo can cost you a full week of labor if it fails on the stand.
Builds magnify the risk repair shops already deal with
A customer-supplied alternator on a routine repair costs you an hour if it's bad. A customer-supplied set of injectors or a knockoff turbo on a build can cost you days, because the part failing might not show up until you're mid-assembly or on the dyno, and by then you've got labor sunk into a part that was never yours to warranty.
If you allow it, price the labor as if you sourced the part yourself, with zero discount, and make clear up front that any failure found during install or testing is billed as new labor, not covered by you.
Reserve the right to reject the part before you start
Give yourself an out in writing: if a customer-supplied part looks wrong, counterfeit, or doesn't match the spec you quoted around, you can refuse to install it without breaching the build agreement. This matters most with online-sourced turbos, injectors, and tuning hardware where counterfeit and gray-market parts are common in this space specifically.
Inspect anything customer-supplied before it goes on the bench, not after. A five-minute look at fitment and part numbers up front saves you from finding out three hours into assembly that the part is the wrong spline count or wrong flow rating.
Set the expectation that your build quality reputation rides on the whole car
Even when the failure is clearly the part's fault and not your work, a blown build with your shop's name attached hurts you in this world faster than in general repair, because performance and diesel customers talk in tight, active online communities. Weigh that reputational risk against the labor margin you're giving up by declining customer-supplied parts on anything performance-critical.
Customer-supplied parts waiver for build work
CUSTOMER-SUPPLIED PARTS ACKNOWLEDGMENT (BUILD) Vehicle: __________________ Build: __________________ Customer-supplied part(s): __________________ I understand and agree that: 1. [Shop Name] did not sell this part and has not verified it is genuine, correctly specced, or free of manufacturing defects. 2. [Shop Name] reserves the right to refuse installation of any part that appears counterfeit, damaged, or mismatched to the agreed build spec. 3. Labor for installation is charged at full rate with no discount for the customer providing the part. 4. If this part fails or is found defective during assembly, testing, or dyno tuning, disassembly, diagnosis, and reinstallation time is billed as new labor. 5. [Shop Name] provides no warranty on the part itself. Customer signature: __________________ Date: __________
Where owners get this wrong
- Installing a customer-supplied part without inspecting fitment and specs first.
- Discounting labor because the customer saved money on the part.
- Not reserving the right to reject a part that looks counterfeit or wrong before you start.
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