You got 4 cylinder or V6?
There are so many ways that the installation can get failed (due to non-OEM head gaskets, incorrect torque, using old head bolts, oil on the gasket/block/cylinderhead,etc., .
So it is unfair to blame the machine shop. A good machine shop will check your cylinder-head at no charge before accepting for the repair.
I did my 4 cylinder (corolla) heads on my own (first timer) and got the head done at a local machine shop. I did 20 K miles already and so far so good. Good gas mileage and better pulling power.
Machine shop charged me $200 to get the head resurfaced, new valve guides, resurface the valves and to install valve seals. They did all other checks before giving it back to me.
Since you have your valves/cams and everything, why you want to spend more on these parts. I saw that site lists a cylinder head for $575. What is the guarantee they use OEM toyota valves/cams and heads?
I think you can get 4runner cylinder head fixed right for like $170 (since it is 3 pistons per side)
Just my thought.