Never use a pool heating contractor who solicits you for your business. Only use a pool heating contractor who uses his name in the title of his company, like me of course. I want a person with a big ego fixing things for me. Chances are they will take pride in their work. Try only to deal with the owner of the pool heating contracting company.
Employees come and go but owners seem to stay around a little longer.
Remember you are trying to develop a relationship. Never chase a special price on pool heater service. There is always something else you have to buy. Ask what the hourly rate is on the phone. When they arrive tell them that you want to know the cost of the pool heating parts before they are installed.