I know there's nothing that can really prevent this, but it's aggravating none-the-less.
I went to an estate sale at a ranch/farm the other day and I have done great at those.
I always make a beeline for the garages, shed, barns first to look for certain tools then I go to the house.
So, I looked in those places, found a few things worth checking out and then went into the house.
The minute I clear the living room a woman walks out of the "office" carrying a boxed laptop (an Acer). She clearly was going to buy it so I asked them what price they had on it. "Forty dollars." She couldn't believe it either.
I walked through all the rooms and came back to the living room where she was sitting looking at it some more.
I started looking something up on my iPad and we started to talk. She had found it in the office, plugged in and running. She said she worked on it for awhile and then boxed it up. I told her I would give her $60 for it right then, but she wanted to give it to her 10 year old grand-daughter !
While we were talking one of the estate sales people came up and said the only thing that was wrong with it was that after 24 hours of them charging it, it didn't hold a charge. That wasn't a biggie to her or to me.
So, my garage route lost me the laptop, but that's the way it goes. It was very surprising the couple had a laptop as their TV was a 12 year old projection type, vhs machine and tapes (no dvds). I would guess it was a present from the kids or something.
Maybe next time.