Michael, who is handsome and projects confidence, says he is an artist who began using the site to find models who would pose nude for him. Craigslist, he said, often fulfills its promise of delivering erotic thrills for a minimal effort.

“I’ve met some extraordinarily beautiful women, had a few extraordinary sexual encounters that made my teeth itch and my brain sweat, put me in states of weird contemplation like, ‘My God, I’ve never experienced that before,’ ” he said.