I've gone to a mechanic ONCE, and that was because the van failed emissions, and I had to get $150 of work done to get a waiver (I knew it wouldn't pass, since it had leaky valve guides...but I was only using it to haul stuff every so often). My bill? "Tested emissions--over limit. Cleaned throttle body. Tested again, still over limit."
$150 please, thank you.
That's why I do all my own work.