In my opinion, it's a minority of people acting badly on purpose. Most people today are honest. But when people get quotes from 3 or 4 companies on a job, most people do NOT contact the losers. Just a fact of life.
If you want to feel better, drive to the ex-customer location. Then drop the clutch at 5K RPM on their front lawn. That should make you feel better.
But not too good for repeat business.
My first reply, I had assumed you were frustrated with competitors. Your frustration is with customers. Just keep on smiling and treat them as you want them to treat you.