To protect yourself, you should only hire licensed and insured flooring installers.
Ask to see both the license and insurance.
Depending on the customization of your flooring project, this should not take longer than a couple of weeks. Some special orders may take longer.
Ask for references and check online for reviews. For example, on Google, Yelp, Home Advisor, their own website, etc.
Does the contractor know all about carpets and the different types of flooring?
Ask many questions to get a feeling for the installers knowledge. You'll know pretty soon how much the contractor knows about floor covering.
Of course, the longer the better. But don't let this be the main determining factor.