When choosing a Contractor in the State of California obviously you want to make sure they are licensed. Check with the CSLB to see who is licensed, ths business name and any salespersonal. There are those who use other companies license numbers so protect yourself. If they have a license then they are also bonded. Lastly make sure they have liability insurance in case they damage your property. How long have they been in business? 

Now to the more important information. Just because a person or company is licensed don't get a false sense of trust thinking they know their trade. It's my opinion that it is too easy for someone to get a license since the state seems to focus on law and take it for granted that you know your trade. We see, repair and redo many systems installed by licensed contractors. In some cases unfortunatly they have already spent the money they had set aside and are simply stuck with what they have been given. In other cases it is just to costly to remedy. 

There are key questions you can ask when getting a quote from a company. Some of these questions have been addressed on our site. Does you contractor do load calculations for proper system sizing? Is your potential contractor familiar with Manual D duct design? What program does he use? If they look at you with a blank stare then maybe you should call someone else. A high percentage of companies do not use these tools, either because they don't know or don't care to take the time. 

Finally trust your instincts. If something doesn't seem right then move on to the next one. Google and Yelp reviews can be helpful but know that there are companies that can remove bad reviews or hide them from being seen. 

The most costly lessons learned are one, a contractor cannot ask for a deposit of more than 10 percent of the total cost of the job or $1,000 whichever is less. This applies to any home inprovement project, including swimming pools. One of the most important things to remember is stick to your schedule of payments and never let payments get ahead of the completed work. I have seen many cases where people give too much money up front and never see the individual again, or pay too much before the project is completed and have a difficult time getting them back to finish. 

For more advise and guidlines go to CSLB.CA.GOV