I'd like to respond to the comment about shops making most of their money from parts sales. That simply has NOT been my experience working part-time for an engine builder and a classic car repair/modification shop.
The owner of the engine shop probably made around 20% on parts, depending on where he bought them (Edelbrock master distributor, Federal-Mogul warehouse, local parts store, etc.) However, he was fine with customers bringing in their own parts. And sometimes Summit Racing's price was not much more than our cost from local distributor! The vast majority of his income was from labor for cleaning, decking, boring, honing, balancing, assembly, etc.
At the car repair/modification shop, we'd give the owner part numbers to order from Summit, Jeg's etc for the major stuff. Then we'd have the local NAPA store deliver smaller parts and incidentals, and make around 20% on those. Again, the real income came from labor charges. As for a parts runner charge, we never would have done that unless it required a trip across town. And even then, we'd try to factor those things into our quotes up front. Quotes for a job were generally whatever we thought it would take plus 10%, because Murphy lives at car repair shops.
Hey, and I take exception the word "goon" for obvious reasons!