Don't reinforce failure; failure reinforces itself. He got his $200 actuator because he didn't want to pay someone to look at it. Now he's spending $200 on a hunch to narrow down one possibility from the list of possible problems.
Since my last post I had another guy come in, saying he needed a knock sensor and gave me a piece of scrap paper that had "the code" on it. I explained that his car didn't have a knock sensor and that what he had wasn't a trouble code but was in fact the part number for a knock sensor. For a car with a different engine. So he bought a TPS and a MAP sensor, priced out a PCM and got an appointment next week to have it looked at. Because he doesn't think the $100 he's spending today is going to fix it. I did tell him that I wouldn't order the PCM until one of my techs told me that it was the problem, though.
I try. Really hard. I told each of those guys that I'd happily sell them anything they wanted to buy, but I'd be happier only selling them the parts they actually needed. They bought the ones they wanted, instead.