Ridley's Cohort said:
Intense_Interest,
You misunderstood my point. It is not a Merchant who would be most likely to offer the good deal. (But in the case of a really really harsh market, why not?)
Nope, pretty sure you just argued that the illiquid market should encourage Merchants to lower prices as well. But if playing mobile goalposts is your own flawed debate tactic, so be it.
It is the Owner who found/earned/stole/inherited the item who is thinking "Gee, I could take 200 for this 1000 gp item now. Or I could make a small effort and I have a good chance of getting 250. Maybe even 300."
Why should the Owner sell the item to the Merchant for 200 so that the Merchant call sell the item to the Adventurer at such a fat markup? Maybe there is an Adventurer out there who would be happy to pay twice or thrice the Merchant's standard low ball offer? Why not put the word on the street and see what happens?
Considering that you've already read the whole "Used Book turnaround" to show that an established buyer is expected to be able to do massive markup in many cases, I don't see where the confusion is here.
Word on the street? You are still arguing from a modern-centric viewpoint. Word on the street is what gets you killed. Trying to do it as a player is a huge metagaming ploy around "PCs face equivalent encounters", so the DM is absolutely invited to throw a grudge-monster Dragon in your face.
So why would anyone rich enough to afford the magic item in question not instead spend it on 100 +1 swords for their army or having the ability to pay those soldiers in his army? Unless they are in desperate need to have a +10 sword of Godslaying, it isn't a worthwhile investment. And considering that you have to get the magic weapon in question from somewhere, is it even worth the risk that the original owner might be still alive? The only people who exist with those confluence of factors are ones that would be powerful enough to break the Point of Light concept, which is against the assumed setting of the rules.
Magic Items are a form of Health Insurance for PCs. Having less of it while you live is a major risk even in making a "small effort", considering that the real price of a magic trinket can go up to the hundreds of thousands of GP and any monster at or above your ability level will gladly kill you for it.
Meanwhile, if you find a stash of 10,000 +1 swords, a merchant would probably ask you to pay him for the amount of risk he is taking, considering that people who like +1 swords enjoy killing other things. It would be much cheaper for a player to convert the whole group into Residiuum, which is still going to be at the 1/5 price range you think is deplorable.
Some small portion of the magic items in existence will have Owners with such incentives. Maybe that portion is 0.5%. Maybe it is higher. Maybe it is lower.
Create a high-magic world with a large enough city, and that means that every day there are some individuals with a huge incentive to go for a higher price. Not so much in smaller cities...but there is always a chance.
Lets build a necessary group of factors:
Heavy Magic
Large City that has a Leadership that allows random citizens to sell any Magical Item to whomever asks
Amount of Adventurers in the world that can access the city in question (that has to be enough to merit a semi-competitive magic item selling market instead of a locked-out protected one)
Rule of Law enough to avoid you or your seller being strong-armed or mugged
Specific demand of your item in question
Then account the chance that the searcher and the finder will ever overlap within the same period of time.
Thats a huge group of assumptions, especially considering that some of them (rule of law vs. free magic item market) are inverse enough to be close to diametrically opposed.
You're hoping that a campaign will be built into not as much of a "realistic" game world than one that kowtows to some game-breaking concept of "fairness".
As for your other points, if relevant, they make strong assumptions about details in the campaign world. Hypothesize that there is a superpowerful Merchant Guild all you want, but there is nothing compelling about such handwaving.
"Maybe there is an adventurer" is the same strong game-world assumption that I posit in the Merchant Guild concept. And because of the Points of Light assumed game universe, my idea of people within a PoL banding together is far more supported than your assumption of multiple, contactable adventurers that are in need of a certain level of magic item.
The historical record may or may not be germane to a particular campaign, but it is immune to the charge of be "unrealistic".
So? "Unapplicable" is a better method to dismiss an argument than "unrealistic", which is what I did.