Every time I spend money on a modern movie poster I can't help but be afraid I could be wasting my money. If I spend $75 on a Beauty and the Beast poster, what if somebody finds a whole box of them in their cousin's basement? Suddenly the poster is worth nothing.
I've done most of my poster-purchasing on eBay. The paper I collect (namely animated movie posters) turn up there most often and I've repeatedly proven myself capable of getting some great deals there, even if every once and a while you get a dud. As somebody who holds out for low prices, I frequently have a long list of posters on my Watch List (in some cases every appropriate result) and have sort of gotten a feel for what a number modern movie posters (1990-onward) can be worth. This expertise is quite limited, and is namely isolated to posters for animated films, but I do feel confident speaking for the small niche I know.
Recently, a seller listed an auction for a John Alvin "The Lion King" poster with a $20 opening and a $30 BIN. In his auction, he includes many detailed pictures of not just the poster he's selling, but the roll of fifty from which he is pulling them from. Before this seller, this poster typically came and went around $40-$50. While his roll of 50 is pretty beat up, he more or less has the ability to dictate the eBay value of the poster as long as he can match the quality of others listed.
After his initial listings ended, he relisted the auction differently now with only a $10 starting bid or a $15 BIN. Clearly well below the previously typical $40 price tag. Assuming all of his posters aren't junk, until he runs out of posters, the market for "Lion King" posters is in his hands, and he has effectively brought down the price and the market.
In the last couple of months I have sent messages to three sellers asking if they would consider letting their "Lion King" poster go for less than their BIN listing and offering $30+ shipping. All three said no. Since then two of the three have sold their poster for what they were asking. In light of this new lot of 50, I received a surprising message from the last remaining seller asking if I would still like the poster for $30. He opened the e-mail with "The value of this poster has gone down".
Long story short, I've seen these "boxes of fifty" before. It happened very similarly with the ensemble poster for "Cars" and "Up" last year when somebody got their hands on 50 posters for each movie left over from an East Coast premiere. I hate it because it hurts my confidence in my value of my collection. I don't really collect as an investment and I don't tend to sell my collection for a profit, but I don't really like seeing my money go down the drain either.
You guys who collect older posters are smart. The world of modern posters is frustrating and stupid. Eventually somebody will probably find 100 Dark Knight teasers and Lost in Translation teasers and they'll be a dime a dozen until they're all bought up. Until then, I'm going to start buying posters I already own just so I can destroy them.