I've worked at 3 shops. Every single shop I've worked at marked up parts, and usually would not install customer parts and if they did they would not warranty them.

That is my personal experience.

 

That's how it is, if they install customer parts then there's no warranty on the parts. But as for marking up the parts, that's a no no! I've had shops try to do that to me and I'll pull out my phone and go to 3 different sites and have them explain to me why there's is over priced. It's a quick way of seeing which shops are trustworthy and which one's are trying to rip you off thinking you don't know about cars.

 

thats one the reasons i like to do my own work and if i dont know i try to learn how. i cant trust any mechanic or machine shop. ive paid 2 differente mchanics to fix an oil leak one ov them ended up bending all 24 valves on my v6 and none of them fixed the damn oil leak.

 

why don't u just lap the valves and install new valve seals urself? there are so many guides and videos out there for it. If you don't need Valve Seats or Guides, there is no reason to send the head out. Just get a Felpro Head gasket sets(w/ bunch of other seals)
I buy Valves from Ebay, and they work fine. To Check your work, all you have to do is spray brake cleaner into the Intake and Exhaust port, if it doesn't leak out of the valve, it is good. If it leaks, lap and clean it again.

Or better, but a reman Cylinder head from a reputable source.