Ah, this is rather timely. I just sold my old tv stand tonight to someone from Craigslist. It's not something I could easily transport at this time, so they had to come to our house. A couple of guys from Minneapolis. They showed up an hour early (luckily I left work really early), and of course I was a little worried that I gave them directions to my house when I wasn't home, but they didn't know if my wife was or not and we have 3 dogs, while not vicious, I'm not sure people would want to mess with them (they put on a good show at least).
They came in and looked at it, commented on the basement and setup. Asked if I'd take $100 for it, I said no, I just dropped it from $200 to $150 a couple of days ago. The guy said he'd take it, and handed me a wad of cash with a $50 bill on the outside. I put it in my pocket while they carried it upstairs. I went back down to grab the drawers and glass top, checked the cash while down there and it was $57.
My first thought was, great, I'll go up there and they'll accuse me of taking the $93 and trying to get them to pay more. I just said 'Hey, the money you gave me is a little short'. They asked how much and I said it was only $57. Their response was, that's not a little short, that's a lot, there should have been 3 $50's but they must have given me the wrong set of cash. He pulled out a white envelope and sure enough there was 3 $50's in there, so we exchanged. They insisted it wasn't done on purpose and was an honest mistake.
Most of my transactions are typically much smaller dollar amounts, so it's not that big of a deal that it needs to be counted (usually like $10-$20). But I've learned my lesson from now on in such cases, always count immediately. And I'm a little wary of having people come to the house for things, but sometimes that can't be helped. I almost always look up the persons email/name/phone number when it looks like I'll be doing a transaction. If they use a work email (like this guy did), and I can find out where he lives and age online, I'm typically ok with it. I just usually tell someone where I'm going and who I'm meeting then, just in case I don't come back...