There are two sides to a coin. Same as handling your business. You can make a quick buck by overcharging but you may not hear from the same customer again. When it comes to services like car repairs, there is no doubt that you may not able to understand how things are being charged. Some charge by hours they put in, some by the complexity of the labor and some my percent of the spare parts involved.

Accident Damage
There are a few ways to tell if the mechanic is sincere when pricing their services. Always ask for a quotation before the mechanic start working on your car. But if the mechanic tells you that he need to charge for checking and analyzing the damage, don't be alarmed. It's is common. Plus, i think it wont be fair if the diagnosed the problem for free.