Just saw this popular mechanics article called "Confessions of a car dealership service manager"
http://www.popularmechanics.com/cars...11261?click=pp
Here is an interesting part:
What's an example of a common tactic by dealers to pad the bill?
So-called shop supplies. That is, and always has been, the biggest crock of crap I've ever seen, and it's been going on for years!
It is essentially similar to going to a nice restaurant, getting your check and finding you've been billed for napkins and silverware, which are necessary costs of the food service business. Shop supplies include, but are not limited to, shop rags, lubricants—this isn't the motor oil, transmission fluid, brake fluid and steering fluid they might put in your car—and the cost of disposing of used oil. These are just some of the necessary costs of doing the auto repair business. Some dealers do not charge for them, but most do, and what is considered shop supplies is at the discretion of each individual dealer.
I've seen a customer get billed for $30 in shop supplies—on top of their estimate—for the use of three shop rags! For that price, I can buy 20 rolls of shop towels at Auto Zone.