Undercover detectives with the Jacksonville Sheriff's Office arrested 11 men offering to do work for them despite not having contractor licenses required by the state of Florida.

JSO, along with the Department of Business and Professional Regulation, arrested the men Friday after their week-long investigation.

IMAGES: Mug shots of 11 arrested in sting

Police say unlicensed contracting may seem like a victimless crime, but they say it's a serious crime nonetheless because many people offering work are out to rip off others, particularly the elderly and the poor. They try to take their money and take advantage of them, which is why police say they're working to get the unlicensed contractors off the streets and get more business to those following the law.

"What they do is they go into these people's houses, a lot of times they have criminal histories, they don't do quality work, and they take that deposit and disappear, and there's nothing these individuals can do," JSO spokeswoman Melissa Bujeda said.

Detectives in last week's sting contacted the suspects on sites like Craigslist. Police said they weren't licensed, but the men offered to do jobs for the detectives that required them by law.

"This is something we want the contractors to know we're out here doing, and it's illegal to do this," Bujeda said.

Chris Simons, of the Northeast Florida Builders Association, says people get scammed all the time using unlicensed workers.

"I've seen some of the most heartbreaking situations where someone of low income or a senior that's spending their last dollars to get something repaired, get that roof fixed, on someone that's not licensed, and they take that money and they don't complete that job, and it's a much worse situation," Simons said.

That's why he says people should check for a license when they look to hire someone, and also ask for references and don't pay everything up front.

"It's very important that you do your homework, you find out who's licensed, who's going to be there tomorrow, and you'll pay less in the long run," Simons said.

To find out if the contractor you're about to hire or have already hired is licensed, contact the Northeast Florida Builders Association on its website or by calling 904-725-4355, or the state of Florida on its website or by calling 850-487-1395. You can access their databases and see if the workers are licensed and valid.