The worst I have ever seen was many years ago when I walked into a house for a pilot not staying lit. You could smell gas, customer insisted to show me how he lit pilot, it flared! Said ,nephew who was taking hvac class at the local community college replaced the thermocouple for him. Instead of unscrewing the easly reachable T,couple from the burner he bent the whole thing around and replaced it and broke the pilot tube (cracked) at the gas valve and the pilot burner. New pilot tube with the customer on my shoulder the whole time. He asked what the problem really was and I explained, and could'nt keep my mouth shut, and asked why his nephew would want to kill him. He became a longtime customer,little dingleberry asked for a job a few weeks later-haven't seen him this last 18 years.