Diagnose engine problem

We brought our sons 2003 Chevy S10 in to find out why it was running so poorly. 2.2 liter straight four. Engine was skipping badly. I just didn't have time to deal with it. I am not a professional mechanic but have been working on cars since I was a kid and I'm almost 50 now. (my dad restored cars when I was growing up) The diagnoses was a blown head gasket and would cost 987.00 to replace. Ok, truck hasn't been overheated and coolant level isn't going down at all. Guess its time to check it out myself. My son and I removed the plugs, looks like valve seals are leaking a little oil but no sign of coolant. We checked the wires, # 2 wire had a short. We installed new plugs and wires truck ran perfect and check engine light went out. It's been 3 weeks since we installed new plugs and wires, no sign of plug fouling. Simple repair. Not sure if the mechanic is just inexperienced or just needs more work but beware!