I go to garage sales sometimes (here they are called tag sales) and a number of times I've spoken to people who have received very high offers for vintage games/systems at their sale. The catch is they made the sale, but the person hasn't come back yet to pay. I'm thinking this may be some type of troll to play with the sellers.
One example a women told me she sold an atari 2600 + 31 games for $400. She was waiting for the buyer to come back and pay. This was at the end of the day so I don't think they were coming back. This system wasn't boxed nor were the games, so I don't see how the value could be that high. I can only guess this is some type of troll people are doing although I can't imagine why.
They are not really trolling per say. What they are doing is telling you how much they want for it by saying its already been sold. That way if you really want it you may offer a higher price and convince them to sell it to you since you are already there with the money.
Wouldn't it greatly depend on the games? 31 games is a lot, and could easily be worth anywhere from $16 to $400 by themselves. If it is all Pac-Man, Yars Revenge, Combat, E.T., Video Olympics, and other commons, then no. But, one or two rares really drive up the price.
It does depend on the games like you said. But seeing as how he didn't mention any games you would assume that the person selling the items did their research and $400 is what they ended up with. Although, it could also be the opposite and the individual only looked up how much an Atari 2600 was being sold for and threw that out there. The problem is that the ball was on the sells side to begin with and they were probably looking for a sucker.