Honesty and reputation. How many times have you gone to a call and folks were told by another Tech. they needed a whole new HVAC system installed, that theirs were "Fried." More than once I have been called to see what I could put them in a new unit for, and I asked if they would mind if I checked their system first. More than once I found their only problem was the evaporator was completely stopped up. Then they candidly complain that now it gets too cold. I like those kind of complaints. Once a shorted control wire was burning up transformers. Oh, you need a new unit they were told. Simple things like this. I went to a call last week to find another company had gutted out the burnt up breaker assy. in a Trane air handle, and just wired it direct. It is still breaker-ed outside, and has a disconnect close by, but its still not right. Sadly, the customers never know. I wouldn't do that in my house. I was always taught by my Dad, "If you can't do it right then leave it alone, if you don't, then find another vocation." You may not make as much money initially, but your reputation will get you invited back into their home, and their friends. I'm not perfect, but I try to do a perfect job.