The number one item to look out for is longevity. Ask yourself how long this provider has been in business. This has two key benefits. The first is that they will have additional expertise. The end result is going to be a superior quality install for you.
Secondly, you know that the supplier is going to stand by their warranty and performance guarantee. A new company might provide a warranty and guarantee but go bankrupt in five years, or the warranty could be completely fake. This can happen when you use Chinese importers or similar quality companies. By simply choosing a provider that has been doing business in your area for many years, you can’t go far wrong.