When it comes to hiring a professional window cleaning company, one of the most important things that you can look at is experience. If a company has been in business for many years and has lots of satisfied clientele, then they must be doing something right. In addition to the company, look at the employees. It is the employees that will be doing the job for you, so it is important to know that they have some experience in their background as well. If there is no information to tell you how long the company has been around, just ask!