Grrr... I am mad for you. That guy was completely in the wrong. Period.
A similar thing just happened to me and I am still steamed that I allowed it-
I held a yard sale, and put out some of my daughters outgrown clothing. In the tote that I was pulling from, there were some very nice, very expensive items (Hanna Andersson) that I decided would do better at a consignment store, so I left them in the bin and slid it far back under the table. Later in the morning, a woman handed me a handful of clothing, and asked me how much- as I was folding and bagging them, I realised they were all the expensive, name brand items that I had left in the bin. I was annoyed, but we needed the money, so I thought, "whatever." I even gave her a ridiculously low price ($2 per item), knowing full well I could get far more than that at the consignment store. She opened her very expensive handbag and said, "Oh, all I have is $X.00, will you accept that amount?" She hadn't even looked in her wallet! I knew she knew exactly what she was doing, and what the stuff was worth. I gave her a hard look but she stared me right back down, and I finally said I would accept what she had offered. She quickly grabbed the bag, and as she was walking off,
she threw two really nice developmental toys into it, and said, over her shoulder, without making eye contact, "Oh, I paid for these too!"
I should have said, "Like HELL you did, theif!" but I was honestly so shocked at that point, that I just stood there in disbelief.
I was swindled by a professional, and I did NOTHING to stop it.
Did I mention that I am still furious with myself?