The department for Trade and Industry has created the following guidelines when choosing your double glazing installer :

• be clear about what work you want carried out. Put down in writing the exact details of what you want done and how much you are willing to spend.
• choose a double glazer that specialises in the type and size of work you want carried out and check they have insurance.
• ask for several written quotes detailing specifically what work needs to be done and the price you will have to pay.
• ask for previous referances and follow them up.
• avoid payiong cash upfront and ask for a fully itemised receipt.
• be wary of traders who call unexpectedly and offer their services - check them out