There are some key things to ask for.
1. A 3 angle valve job gives better sealing and flow, but takes more work than a standard resurfacing. Worth the money.
2. Make sure that if you changed the camshaft, get the right springs to match the cam!
3. If the heads are magnafluxed, it can add more cost but increases the chances of finding cracks over just doing a pressure check. Worth the money if the pricier shop is doing it. No change in performance, but a far superior crack detection method.
4. Do they only machine the valve seats, or also mill the head face too?
5. How much is shipping? Who covers shipping for warranty work?
I'm sure the other guys here will have more info, but that's what I can think of off the top of my head.
My oil line fix
My 100k stopped odometer fix
Brace for impact, I'm in a "modifying mood". Massive thread count inbound.