Customers who "just need a quick look" are my biggest time sink

Had a walk-in yesterday at 4:45pm, guy with a laptop that "just won't turn on." I popped the back off, found a swollen battery pushing the trackpad up, told him it was a $90 part plus an hour of labor. He said he'd think about it and left. But that's not the annoying part, it's the three people before him who each took 15 minutes of my bench time describing issues they could have solved with a Google search and a screwdriver. Last month I tracked it, 6 hours a week on free diagnostics that never turned into paying work. How do you folks handle the lookie-loos without coming off like a jerk, do you charge a bench fee upfront or just accept it as part of the job?