Take it to someone you trust, then watch them. I had my truck tuned up because I'm unable to do it myself. The truck ran worse when I got it back than before they started. I was told that a simple gasket needed replacing at the cost of $14, but the location of the gasket would entail $350 labor. I took it someplace else and they told me someone had switched my sparkplug wires around. That fix, another tune up and muffler repair cost me less that $100 at the new place and the truck runs fine. (My car, on the other hand, got totalled Friday night. Thank God my wife is safe. I heard the crash inside the house and ran out to find it was my wife who'd been run into. Not a good thing for my heart condition.) Get a second opinion if you even suspect a charge might be out of line.