Just a dust - why so serious?

I got call from service point telling me that I could now pick up my computer. They've cleaned the interior from dust. Normally this type of service would cost me but they forgot to tell me this so this one is free of charge.

Why was I not convinced that this is the solution? Even though they said that they tested and saw no more than 70°C on CPU temperature.

I brought the computer home and fired up two "yes > /dev/null" and soon saw temperatures above 100°C. Why did not they test my computer properly? Was they on a hurry?

I soon visited service point again... this time without any hopes of facing expertise at the other side of the service counter.

Week... or two later I return to pick up my computer. New motherboard (Logic board) installed and this time they tested it 24 hours with Apple hardware test and it did not overheat.

I was not surprised to see that nothing have changed... Still every game is unplayable because of massive FPS drops due to CPU's temperature throttling. I have a nice 2,8GHz CPU which is usable only on light usage. When I try to push it to the limits it just regresses back to 2005 when I last had this slow CPU.