Law enforcement agency parking lots are becoming a modern marketplace.

In the era of Craigslist and other online classified ads that offer secondhand deals, Twin Cities metro area law enforcement wants to make sure transactions don’t turn into opportunities for predators.

Hennepin and Anoka County Sheriff’s Offices are the latest departments to invite citizens to complete their transactions in their parking lots, or even to come inside their lobbies. The idea is that legitimate buyers and sellers won’t mind carrying out their deals on camera footsteps from police officers.

Maria Lerohl, who listed two diamond rings on Craigs­list Wednesday with the caveat in her ad that she’d like to complete the transaction at the Anoka County Sheriff’s Office, said the new arrangement “makes you feel a little bit safer about meeting a stranger.”

When the Anoka resident heard about the new exchange zone recently, “I thought, ‘That will be perfect, especially for something like this,’ ” she said.

Craigslist alone has 60 million users each month who post 80 million classified ads per month.

“This is a nationwide trend,” said Anoka County Sheriff’s Cmdr. Paul Sommer. “A lot of law enforcement agencies are doing them. We wanted to let people know it’s OK to use our facility for that.”

Anoka County’s “Exchange Zone” is at the sheriff’s headquarters on Hansen Boulevard in Andover. The parking lot is well lit, with security cameras rolling 24 hours a day, an emergency call box and deputies working in the building.

Anoka County Sheriff James Stuart has extended the hospitality even further, saying people are welcome to carry out their transactions inside the public lobby from 8 a.m. to 4:30 p.m. weekdays.

In July, the Hennepin County Sheriff’s Office established three “Swap Spots” in the lobbies of its three buildings in Minneapolis, Brooklyn Park and Spring Lake.

Sommer said people have been using the sheriff’s parking lot for such transactions for a while, but act like “they don’t want to be a bother.”

“We’ve noticed a lot of child-custody exchanges take place in our parking lot. I have seen housewives exchanging baby goods,” he said. “People go to the back of the lot, out of the way.”

Newly erected signs now direct people to a more visible area of the parking lot. “This is the area where we see things best on the video camera,” Sommer said.

He cautioned, though, that staffers won’t necessarily be monitoring those security cameras in real time and people should still be mindful of safety. The exchange zone is “an added measure of safety,” he said.

Lerohl said she and her teenage children do occasional online buying and selling, and “I have told them I don’t want strangers coming to our home in that situation unless I am there. … There is always that unsettled feeling about a stranger coming to your home.”