What was dodgy enough about him to make you think he wasn't in the market for a bike? That aside, if he thought it never got used and wanted to buy it, sounds like what you'd do, right? If you were going to steal it would you make the owner aware
Although, I am paranoid too, and I would be concerned that anyone had noticed it. I'd be moving it, not leaving it there, it's doubtful you'd stay awake all night?