The mechanic will tell you, "Fine. Go to the average costing mechanic then." At that point it will be up to you to find him.

A busy mechanic will give higher quotes because he doesn't need your business. His worker utilization is high, and that is what drives his profits. Markup on parts is small, if not zero. Taking on the extra work means he has to bring a guy in on Saturday, usually his best and highest paid one, and pay overtime.

Now the idle mechanic knows the market rate and will quote that or lower, based on how much he needs the work. But there is a reason that he is idle.