El Vader,
Perhaps you would answer the following questions for me?
What percentage would you feel is fair?
Should the percentage be the same across all items purchase to repair or maintain your equipment? Should the percentage for a $30 of parts be the same as a $100,000 of parts?
Do you think that a group of people should be able to vote what you should earn or should you be able to market yourself to earn as much as someone is willing to pay you?
Last, if you decide the amount someone wants to charge for their services is too much! Are you able to elect not to use them?
The standard is the same you use in determining your pricing. It's what ever the market will bare.
It sound like to me you wish to keep your expenses down and your profits up!
