One of the problems, I think, is that everyone is focused on the vending system. That's good to a point but it's bad for the game. An example is: Having high prices on a small amount of vendors vs. having alot of vendors with low prices.
In this example, we have less people playing the game when there are high prices and more people playing the game when there are low prices. So, you have 2 economies, the people playing the game and the number of people playing the vendor system.
Another problem is, the high end, being the rich, they have less need for the item. So, as the vendors become less and less, the items themselves will become less and less important to have. An extreme would be 2 people left in the game trying to sell tinker legs to each other at 80 million and already owning 4 sets each.
I would suggest allowing people to create vendors that supply basic needs, which work into the skills, such as crafting skills. An example: Acid Rope or Bandages. These are not 80 million dollar items but they are very important to the characters.
The problem is, if you set up a vendor, you will lose money. So, not only have you done alot of work supplying the vendor, now you can't even sell the item and on top of this you're losing money. Another example would be, repair deeds, potions, tools, looted weapons, maps, a very large list.
Most of these things, you would not sell for more than 100,000, probably not even 50k. So, why not allow anything placed on a vendor to be 1%, if it is under 50k. If it's 100k, let it be 2% and anything over 150k could be 6%
and anything over 1 million could be 8% and anything over 10 million, 10%.
This would force high end items to be sold through chat and allow low items to be stocked. Why would somebody place bandages on a vendor to sell as storage, if they could simply keep them in a chest and if people are going to place very high valued items at low prices they're going to sell.
If people can afford to put very high value items, like 80 million, then they can afford to pay just about any penalty, in my opinion.
It's amazing how it seems to become a discussion of the rich and powerful, rather than focusing on how to create a vendor system that supports more vendors rather than a few rich vendors.
Also, a system should be put into place that randomly buys items from vendors, so that every now and then, the system will buy an item from you, especially if it's a list of items that are low profit.