A police sting at the Maine Mall Wednesday led to the arrest of three men on charges of prostitution.

Police say arresting customers, or johns, is an important tactic in trying to stop sex trafficking.

“There are several prongs to this problem, and targeting the demand side of the industry is just one of them,” said South Portland Detective Sgt. Steve Webster. Often, the women involved in prostitution are being forced to participate and face physical and emotional abuse if they try to refuse, police say.

South Portland police, Cumberland County sheriff’s deputies, Gorham police and the Homeland Security Human Trafficking Task Force participated in the operation.

Three men responded to an ad placed on social media and met with an undercover officer planning to exchange money for sex, police said.

Police charged Thomas Kahl, 64, of White River Junction, Vermont, Willard Putnam, 56, of Windham and Robinson Rich, 25, of Cape Elizabeth with the misdemeanor charge of engaging a prostitute.