At the time he seemed honest enough, but later, after I'd given him the money, I realized it was a put-up job.
put-up job
A deliberate attempt to con or deceive someone. The want ad ended up being a put-up job designed to scam money from unsuspecting victims.
a ˌput-up ˈjob
(British English, informal) something that is planned to trick or deceive somebody: The whole thing was a put-up job. He set fire to the shop himself so that he could claim the insurance money.