dam this $hit is whack.
personally, it's a risk, but i wouldn't get the cops involved. send him an email saying you're interested in the products and want to come by to check them out and will purchase them if everything seems to be working correctly. arrange a meeting in a public place, but make it somewhere that he can't quickly get away. try to get him on foot away from his vehicle. chances are it's just some punk teenager that was looking for an easy steal. confront him about the situation sternly, and threaten to call the police and press charges once you get his name (do this once you get the radar detector in your hand as you are examining it for damages). bring a friend that can come at him from a different angle for backup in case you need some help confronting him. work out a "sign" between you and your partner so that your friend knows when to walk up, but make sure the equipment is yours first obviously. you could make the sign something like scratching your head in an unusual way or something.
if it turns out that this guy is a lot bigger than you, or if the situation looks kind of sketch, then just look at the items and say you didn't have cash today, but can get it tomorrow cuz you're waiting on a transaction or something, and that you just wanted to make sure the products were in quality condition before you wasted your time tomorrow getting the cash ready and all tomorrow (make up some excuse like you got a wedding to attend that's not in town, and a radar detector for the long drive would save you some time on the road or something). then contact the police and press charges. an escort passport isn't a cheap piece of equipment, and is worth the hassle of pressing charges.
hope this helps.
edit: also, make sure you act quickly on setting up a meeting so that no one else tries to buy it first.
