CONCORD -- An Oakland man who tried to warn his colleagues about a sting operation from the Contractors State License Board was among 15 people cited for contracting without a required state contractor license, the board announced Friday.

The board's Statewide Investigative Fraud Team conducted the investigation at a residential house with the assistance of the Contra Costa County District Attorney's Office on Wednesday and Thursday, according to a news release.

Investigators sought bids for painting, concrete, fencing, landscaping, and tree work from suspects who were contacted through business cards, ads in online bulletin boards, including Craigslist, and complaints filed with the board.

Oakland resident Moises Galban Zamora refused to follow instructions to avoid telling others about the sting after he had been previously arrested on two illegal contracting charges, according to the news release, and he was slapped with an additional citation for resisting a peace officer and driving without a license.

Fourteen other contractors from cities across the East Bay, including Pleasant Hill, Antioch, El Cerrito, and Richmond, were cited on misdemeanor charges for contracting without a license. Ten were also cited for illegal advertising because they did not include their license number in their advertising -- a state law. Two individuals were cited for requesting an excessive down payment -- the appropriate amount for a down payment limit is either 10 percent of the project's cost or $1,000, whichever is less, according to the license board.

Also, one citation was issued for failure to have the required board Home Improvement Salesperson registration, the news release stated. According to the board, it is a misdemeanor for any home improvement company salesperson in California to write contracts for their employer without being board registered.

Contact Katie Nelson at knelson@bayareanewsgroup.com or follow her at Twitter.com/katienelson210.