"He has recently stopped installing any and all customer supplied fixtures."
What's new, auto repair shops, and just about every other repair business refuse to install customer supplied parts, and for many good reasons, one of which is they loose the very thing they are in business for needed profits from material mark-up.
If you are forced to use customer material, don't forget to make up the loss, by an increase in labor charges.
Bottom line, you are in business to do better then just working for an hourly wage, and paying your expenses.
