There's two mentalities; as buyer and as seller. At the moment you are in buyer mode. When the time comes to sell that nice Revenge poster you have, then a switch will flick in your head.
True, but within reason.
For example, a week or so ago on Storage Wars (yes, I like the show), Barry found a Revenge crew jacket. Very cool. Anyway, he went to see some "hollywood memorabilia experts" to get it appraised. Long story short, they mentioned the Revenge poster and said that they start at $5000. Now, we all know that simply isn't true. In fact, they didn't even differentiate between the dated and undated versions. But, I know enough to know that their pricing is utter BS. Even Dave doesn't try to sell them for that much. Fortunately, even if someone was foolish enough to have one, watch that episode, and think "OMG, I'm going to sell mine for $5,000!", there are enough of these posters in circulation with historical price data to hopefully set the record straight.
However, with this poster, the latter isn't the case. There is no record of selling prices for similar ones (at least documented that I could find), so the seller had to go solely on their sentimental value as well as what other "Experts" told him it was worth. And the "Experts" he spoke with gave him five-digit values. Apparently he also tracked down other owners who said that their posters were worth $15,000. But, notice that none of these so-called experts actually offered to buy it for that amount. And when he put it up for auction, he made his description clear that all of these high-rollers were going to be fighting over it, which probably scared some people off.
In the end, I think we really don't know what the true "value" of this poster is. I think if it was listed again, with no reserve, and a less.....threatening?....description, and the market was able to make a determination, then we would have an idea what it could actually go for.