Licensed & Bonded:
Check to see if the company is properly licensed or bonded.
Liability Insurance:
Ask to see proof of contractor's liability insurance coverage, making sure the coverage is up to date.
References:
Look for a company with a proven track record that offers client references. Talk to the customers to find out whether they were satisfied.
Better Business Bureau:
Are they a member of the Better Business Bureau? Generally, if they don't want to be accountable or tracked, they won't join. Contact the Better Business Bureau to check for a business report on the company.
Up-Front Money:
Don't give them any money until the job is totally completed. Some contractors have been reported for taking a percent of the money down for a partial job, and then never returning to finish. There is an exception when purchasing a new roof. Sometimes a percent is required when purchasing material.