It is both what the buyer would pay and what the seller would sell for.... This is further complicated in an auction setting especially with say Bruce's .99 auctions buy really being what Buyer 1, Buyer 2, Buyer 3 and Buyer 4 would pay for it.
As an example let us say we had 4 buyers:
Buyer A was maxed out at $50
Buyer B was maxed out at $80
Buyer C was maxed out at $30
Buyer D was maxed out at $40 because a nat shat on the upper left corner; normally he'd be maxed at $60.
So Buyer B wins.
Now the same poster comes up again. This time the poster is beyond mint perfect example. Same four bidders:
Buyer A was maxed out at $50 isn’t concerned with condition.
Buyer B was maxed out at $00.00 - he out already has one.
Buyer C was maxed out at $30 still trying to buy it on the cheap not really an “A” list poster.
Buyer D was maxed out at $60 he’s back in at his amount because there is no defecation
So Buyer D wins right?
Nope! A newbie joined APF saw the poster and with all the new money he has since he hasn’t bought anything, period, trumps them all with a $100 bid. He has a general idea and wanted to make sure he got it.
So here we are again for a third example: Now the same poster comes up again. And so on and so on…
As T suggests, if you are willing to wait long enough and bid each time one becomes available, your chances increase. You can obviously increase you max to win it sooner, but then the other guy that has been waiting two years for it decides he can spend $10 more on it this time and his max resets.
If we want posters at reasonable prices, in theory we should set a price we would pay and never waiver because every increase in our price impacts other desiring the poster. Now, what wasn’t discussed is fall out from buying from other venues etc. You can get very good deals where there is no competition. You can get the subject poster for $30! So the odds are more in favor of just sticking to a price over the long haul (perhaps adjusted for inflation) and/or searching for it off line, eliminating the competition and falling back to what a person is willing to sell for… You will eventually get it for your price or less, as long as there are not too many newbies entering the market and/or you catch a poster dealer having a bad month.
And since I am on the topic of Newbies, APF actually impacts the prices we pay for posters. For example, before joining APF I was not much of a Japanese poster fan. But, as I was exposed to them through the forum, I have purchase many more than if I had not joined. I would have kept chugging along working on my Eastwood 1sheets… The forum created competition for its members!!
So the moral of the story is don’t tell anyone about what your bidding on, try to make as many offline (out of public view) deals and make sure to advertise every acquisition as to encourage others to spend their money on the posters you already have!