What is fixed and scarce however is land (you can claim plots and build houses, shops etc). Would having a server with land tied to a token make sense or is it a bad idea?
If A is worth 10x in an auction you pay 10x as much in fees. This works best if players buying and selling is a regular part of game play such as a complex crafting system where sub components are traded and someone can focus on making them.
Alternatively, professions can have some useful waste for another profession. ie: Making an epic sword needs 10 blue and makes 5 green, an epic boot needs 10 green and makes 5 blue. Meanwhile you get 1 red and 1 blues per ore. So, now your weapon makers and your armor makers will be trading their waste. Downside is guilds can become self sufficient.
PS: As an analogy, the USD has value because people must pay taxes on value created in USD. This instantly creates trillions of dollars worth of demand each and every year and continues to scale with the economy.