Any dealer who does not have a state contractor's license.
Anyone who wants more then 10% total job cost up front.
Any dealer that does not give you a written quote.
Dealers that run large yellow page or newspaper ads that say they sell all brands or list brands only by name and not logo.
Manufacturers can stop dealers from displaying their logos but cannot stop them from using their name. Large yellow page ads and newspaper ads are very expensive, especially in large cities. This expense can only be recuperated by charging you more money in installation or service.