I can think of a couple off the top of my head.
1. HO called about hearing water running but not being able to find the source. When I arrived I could hear the water, I followed the sound down to the basement bathroom and turned off the tub faucet.
2. HO called " I just vacuumed out this furnace I bought from you last year and now it won't work. Get out here and fix it now!". I went out, put the blower door back on and voila! the furnace worked again. I explained how the interlock switch on the door keeps HO's from injuring themselves as I wrote up his bill. 1.5 hours travel, 1 hour labour minimum, plus mileage. I knew what the problem was when I was on the phone with him, but hey, he wanted to be an ass.