Yes, there's many reasons why I don't install customer supplied parts. I've had a couple cases where they bring in their own stuff and want me to install it. After the car is apart, we found out that the supplied parts were incorrect. Now what do you do? The car's apart taking up space in the shop, while you have other cars to get in and get done. Some shops will actually charge the labor rate for each hour that it occupies a bay, since other work (people who are buying the parts from you as well) is getting delayed. If you can actually find a place that's willing to do this, stick with them, because not all places will. Also, any kind of warranty will not apply, needless to say.