Haha all spark plugs are the same? Your an idiot whoever said that. The reason he wouldn't put your Bosch plugs in isn't because he was boosting his income, but rather covering his *** for any future problems. All GM vehicles come from the factory with AC Delco plugs, Fords come with Motorcraft plugs, and Dodge come with Champions, as far as American vehicles go. So, as the saying goes about a good running car, "it runs just like the day it was new", for this to be true don't you think you would want factory original parts? Bosch plugs are not as good performance wise as an AC Delco plug in a GM vehicle. So by him not putting the lower grade plugs in, he doesn't have to worry about the plug not working and you coming back on him for it. The only thing you could be upset about is the $60 extra you were charged for the Delcos, since they usually are about $7 a piece and your car would take 6 so $42 isn't quite the same. However, the Delco plugs should last a lot longer so I wouldn't be to mad if I were you.