How Not to Get Ripped Off at the Repair Shop

The first few times I went to the dealer to get maintanance done on my car, they tried to convince me to do more than was really necessary. They never said my car was broken when it wasn't, but they did try to get me to change things (like spark plugs) that were no where near in need of attention. The last couple of times, though, I've forgotten to take my textbooks out of my car and left them on the front passenger's seat. It's a bit more subtle than handing them my business card to say "hey, engineer!", but it does make them think twice. If I ever go in for non-routine stuff, I'll have to remember this trick in addition to prepping by using my OBD II diagnostic computer. Hehe.