"Ask a contractor the following question to size him up. However always contact two to three contractors to get multiple quotes. Select according to the prices, type of services, knowledge-level, and experience. • What is you length of experience in installing solar heaters or solar power systems? • Would you maintain and service the model on regular intervals that I am purchasing? • Could you give references of past customers? • Is your company licensed or certified? Some of the states of the US require solar contractors to hold valid license. You can contact the state’s contractor licensing board to know more about licensing needs. In case you have decided to hire a contractor, the licensing board can give you more information about him. It can tell you about any complaints against state-licensed contractor."