Having looked back through the thread it appears to me that there is very little learned by comparing different sectors in the service industries
"I ran car repair garage for 15 years and had to give estimates for all jobs, if did not what the problem was to start with i would take a look and once i knew i would inform customer of the cost."
At which time you had possession of the car and it was clocking up a bill just for being in the garage, how many of us have had the "Gun to the head" feeling when we got that phone call?
Any problem with a customer paying you keep the car, the reality is we can't stay in a persons home preventing them from using the boiler or the parts we have fitted.
"I have had issues in the past, and my girl friend, whose flat it is, was ripped by the people who fitted boiler and one on another occasion who claimed to know what wrong, but did not and tried over charging her.
She evidential found a good engineer who fixed it, he did give her a price once he diagnosed the problem."
It appears from your own posts that you have tarred everyone in this industry with the same brush, a question that arises is why not employ the "Good Engineer" again?
Despite how this thread may read to consumers the majority of the people in this sector are neither cowboys or stupid, one overcharged visit to a particular property / customer is not how we build a business, we want the same consumers calling us at least once a year to service the appliance and to continue calling us for breakdowns and the ultimate boiler replacement.
We also want them to supply our details to friends and family and to bring our contact details with them should they move home, they are our wants.
We need the consumer to trust us, I have attended four breakdowns this week where money has not been mentioned, (reminds I should be doing the invoices not typing here), the reason money was not mentioned is the customers trust me, even when I do have to advise about expensive parts the job gets done because I will not leave a customer without heat they will pay when they can (I hope).
Trust works both ways, one thing left out of the original diagnosis was a possible PCB fault I know that if I present the PCB as the problem the customer will most likely doubt my findings simply because he hasn't seen a similar diagnosis on the internet.
So now i ask me, would I want this customer?
Guess the answer.