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You'll certainly want to ask them this. Steer clear of any company that is not insured in California, because that means that any incidental damage they may do on your property will be a real hassle to recover compensation for. It is never wise to work with uninsured tradesmen of any kind. Most states also require that someone have insurance in order to be issued a trade license. If they say they're licensed but not insured, they're being less than truthful.

This is very important, since an estimate is just that. Many contractors will submit a "paper estimate", meaning they've written the estimate down on paper. The bill is the true amount owed and will almost always say "Invoice" or "Bill" at the top of the page. The bill should also list the date it was issued, the due date of payment, and a list of services rendered.

Some companies may require a 10% deposit, some may not require any. For larger projects, you'll almost always need to give a deposit, and it's good to ask how much the deposit will be before going forward with a project. The North Hollywood contractor will know how much they need for a deposit when they've given you the estimate, so ask early.

Always ask for references, and always check them. Keep in mind though that the only references you'll get are people who the contractor is certain will give him a good review. You'd also be well advised to check online review sources in North Hollywood as well, which will give you a broader view of customer satisfaction for a given company.