That's a business permit that anyone can buy. It's not proof of competence. Unlicensed contractors have been known to put fake license numbers in their ads. Contact B.P.R. to make sure the license is valid. B.P.R. can also tell you if there are any complaints on the contractor's record.
Some counties require their own licenses for jobs like painting.
Ask for proof that the contractor is bonded and insured. Check references, preferably with people who had similar work done. You might also talk to local building suppliers about the contractor's reputation. Find out how long he's been in business under the same name. Ask for a clear written estimate, including brand names and the quality of the materials.