There's the rub. When you do a service change, it is common for circuits to be overloaded- something indicated by the over-size fuse. You, being a consciencious type, size your breaker to the wire.
Now, it's quite possible the customer will not believe you when you explain the problem to them. Perhaps they don't think there will be a problem= or, they'll have the work done by some "production shop" that says nothing about it when they quote their lower price.
Of course, their new breaker will start tripping. If you did the work, you get to say "I told you so"...and contract for the additional work. If the other guy did it, he's likely to say "not my problem,"...and the now angry customer calls 'the nice man who seemed to know this would happen'....and you contract for the work.
Naturally, it costs more to fix it in two visits, than had it all been done at the same time.
We can't let our work be treated like a commodity. There are three kinds of work: quick, cheap, and good. You can choose to be any two of the three. The guy who is cheap only will be neither good nor quick.
These are the reasons why I won't quote work "blind;" I want to look the job over first. In my quote, I am careful to specify what I will do. This is not simply tail-covering....it is another opportunity to sell the customer on what I'm offering that the other guy isn't.
The "cheap" guy may make a splash at first...but his lack of profit won't cover many call-backs, and unhappy customers are not likely to be repeat customers.
