It always pizzez me off when I see a "shop charge for materials" or "Misc shop".... sometimes based upon a percentage of the total bill.
I REFUSE TO PAY IT! ALWAYS!
They will tell you that it's to recover the costs of paper towels, hand cleaner, WD40, etc etc that is used in all repairs.
I tell them it's because they don't know how to account for the cost of doing business... and I WON'T PAY IT!
It's no different that the café charging you for napkins, salt/pepper, or catsup.
It's BS and I WON'T PAY IT! It's the COST OF DOING BUSINESS. IT'S THE TOOLS OF THE TRADE!
They ALWAYS take it back off the invoice. If we'd all refuse it, they'll quit that B.S.