UNION CITY -- Nearly 100 people, including about a dozen Bay Area residents, face potential criminal charges after being arrested during a statewide undercover sting targeting unlicensed contractors.

Fraud investigators from the Contractors State License Board conducted stings on Wednesday and Thursday in Alameda, Los Angeles, Monterey, Placer, San Diego, San Luis Obispo and Sonoma counties. Investigators posed as homeowners seeking bids for home improvements including painting, tree trimming, gutter installation and water heater replacement.

A total of 92 people, including 14 who bid on work at a rental home in Union City, were arrested on suspicion of contracting without a license, board spokesman Rick Lopes said Friday.

"Their goal is to fly under the radar, to pay workers in cash under the table and to not pay taxes," Lopes said while standing outside the home in the 3100 block of Chimney Court used to bust the bad contractors.

Investigators contacted the suspects after finding them online at websites including Craigslist, in fliers left on homeowner's doors or by word-of-mouth from legitimately licensed contractors who knew their competitors were not licensed.

Loren Reed, with the California Department of Consumer Affairs, said investigators put out bids at the Union City home for outdoor repairs including landscaping and fencing. Inside the home, they asked suspects to bid on items including plumbing, carpeting and heating.

When the suspects arrived at the home to bid on the repairs, investigators asked for proof of a contracting license. When they could not provide one, the suspects were arrested, Lopes said.

In one instance, Lopes said, one suspect presented a fake, plastic license ID card to an investigator. The investigator knew better and the suspect was arrested.

Under California law, any job estimated at more than $500 must be performed by someone with a state license. State law also requires contractors to place their license number in print, broadcast and online advertisements. Those without a license can advertise to perform jobs valued at less than $500, but the ad must state that they are not licensed.

State authorities said the stings also were aimed at catching a number of suspects on a "most wanted" list of known violators. Warrants have been issued for the arrest of people who appear on the list, who Lopes said are unlicensed violators known to prey on unsuspecting homeowners. The list is available to the public at http://www.cslb.ca.gov/generalinformation/newsroom/mostwanted/.

Included on the list is Khalid Muhammed of Oakland, who is wanted on charges including fraudulent use of a contractor's license, grand theft and soliciting excessive down payments.

Lopes called Muhammed a serial offender known for scamming homeowners throughout the Bay Area. He has more than $200,000 in arrest warrants lodged on him and sometimes uses the business name First Impressions Painting and Decorating, but officials have been unable to locate him.

State authorities recommend homeowners hire only licensed contractors and ask for references.

In most instances where homeowners are misled, the unlicensed contractors don't complete the job or sidestep the job and perform poorly, Lopes said.

"It's not just as simple as hiring someone who will do the cheapest job," Lopes said. "You never know what kind of work you're going to get."

Another tip: Make sure any contractors have proof of workers' compensation insurance.

"If someone (a worker) falls through your roof they could come after you for potential medical bills," Lopes said.

In the end, homeowners may have to pay twice for the job if they have to rehire someone to come in and complete it or make repairs, he said.

Contact Natalie Neysa Alund at 510-293-2469. Follow her at Twitter.com/nataliealund.