First and foremost, the installer should be a licensed contractor with the state of California. Contact the Contractor’s State License Board to verify license status and to ensure the company does not have significant unresolved complaints. Select a company with a proven track record of experience. Faulty installation can be disastrous. Companies that have been in business for a long time often demonstrate experience and stability. An experienced local company is familiar with the local building structures and codes. Many horror stories have been told of customers hiring non-local companies and then never seeing them again. If a problem arises, the customer is tasked with obtaining a contractor or other window company willing to take on a problem of another company. References from others, of course, are important.