if for example you are looking for double glazing in Bristolthen simply type in double glazing Bristol into google and press search and on the first page of google you will get a list of companies and the google local is always a good place to look as you can see the companies local to yourself and ofen there will be reviews on that company by customers of theres. You can try other sites like Free index pagesand also Bizwiki bussiness directory most companies have a profiles on these two site where customers can post reviews .
Always vet the Double glazing company and ask to see there work where you can perhaps talk to a couple of there previous customers.
All double glazing installers should be part of the fensa schemeand they should all offer an insurance backed guarantee, the insurance backed guarantees are put in place to protect the customers. the insurace backed guarantee covers the you in the event that the double glazing company that you placed the order with goes into administartion. and if this happens then the insurace backed guarante not only covers your deposit if the products have not been installed, but also cover the products if they have been installed for the remainding time of the 10 year guaranteeand .
Never sign up for double glazing windows or a conservatory on the first night of the quotation always vet them first most reputable companies will welcome this if they have nothing to hide..