I sold a viewing sphere to a lady on Craig's List about a year ago. Just the other day, she e-mailed me a photo of her fish up inside the sphere, viewing the world, and also gave me an update on the baby fish I gave her, who are growing and doing well.
On the other hand, I arranged to sell some metal water meter covers (I had used them as stepping stones) to a couple, and told them I would be home after swimming at the YMCA, and that they covers were on my driveway, and we could meet there at 10:00am.
Well, I was home earlier than that, and heard an odd noise, and opened up my garage door to see the people with a trailer backed into my driveway, and every single one of the 35 meter covers was already loaded into their truck. The man muttered, "We were trying to be quiet, so we wouldn't wake you." Then the woman quickly (let's say guiltily) thrust the $50 into my hands. Obviously, they were hoping I wasn't home or wouldn't hear, and were thinking they could make off without paying for the meter covers. They almost succeeded.
I didn't let on, though, and we chatted nicely, and they even took some of my fry from last year's spawn. But it was a learning lesson to me - never let people know your for-sale items are where they can be accessed without paying.