depends on the car. we had a problem with the electrics on our Renault; took it to a mechanic in Drogheda and he recommended an electrical mechanic, so we took it to him, up near Mell. He had the car for 2 weeks and could not find the fault. We got it back and it cut out again that day and would not start. We had the car towed back up to the electrical mechanic but he still could not find the fault. Charged us almost 200 euro not to fix a thing.
Eventually, took it to the Renault garage Blackstone, up near TLT & Tesco and they fixed it within 2 hours and it has been great since.
So it depends on the make but if you can take it to a garage that specialises in the brand of car you have thats probably best and they are more likely to know what the problem is. Especially if it happens on other cars in the range, they will know about it before other garages who do not specialises in particular brands.
We go to Blackstone all the time now, the guys in there are great.
HTH