I've put a couple of things on FB Marketplace and soon had people sending the "Is this still available?" question. For the first one I answered "yes" then after a delay I got a message that sounded very like it was a bulk send, which confirmed my suspicion that this was a scammer - just someone wanting to harvest my address, with no intention of ever collecting the item. For the second one, I haven't yet decided - he has said "I live in [my area] and can collect quickly" so I've asked for a day/time, but haven't yet given my full address. His FB profile is not public, and he is wearing a motorbike helmet in the picture, but he may just be protective of his privacy, as I am. How can I politely verify that he is genuine before I give my address?