Many years ago, one of the local TV News shows in NYC did an investigative report looking to catch dishonest appliance repairmen. In this particular segment, they took a central A/C unit and just disconnected a wire that shut the system down but would be very obvious to even the most basic repairmen. Then they had the lady of the house call various repairmen. When they would show up, she would say basically it was working fine, it just stopped all of a sudden, the unit is on the side of the house but I have something on the stove right now. So, take a look at it and just knock when you're done. Out of the ten they called, most were honest. Some reattached the wire and did not charge anything. Others fixed it but still had a basic charge. One guy however, took it to the next level. He urinated all around at the base of the A/C unit and then went and told the homeowner that she had a leak in the system and it would cost approx. $2000 to fix it.
Of course, all these inspections were caught on hidden cameras and the reporter would literally come out from hiding in the bushes and present the video evidence to the lying, stealing cheats. Good television!