I personally have never heard of breaking a plug in before you install it. I just check it to make sure it id not bad from the beginning. As far as burning plugs out, how much of a temp difference was it from when they tuned it for you to the time you ran it and blew plugs? I it was hot (say 80 degrees outside) when they tuned it for you and the temp dropped 15 to 20 degrees and the ran it without retuning it, then you were probably running it to lean and that was what caused your plugs to burn out.