A guy at the AutoZone in Mesa talked me out of a $90 part and I still think about it
Stopped in for a new alternator for my 2004 Tacoma and the guy behind the counter, Marcus, asked what made me think it was bad. I told him the battery light kept flickering at idle, and he popped the hood right there in the lot, checked my ground strap, and found it was loose and corroded. Ten minutes with a wire brush and he saved me the whole job, so what is the best free diagnosis a parts counter person has ever handed you?