@_Lucypher I do like the idea and I don't mean this in a bad way.
I will start off why it wouldn't work in my eyes or maybe you can help answer my questions then. :)
1) Due to the popular demand of Flux, this will overpower the market and make it to where players cannot really trade items due to a market place. Unless your saying that when i sell my 6* mask that in return i'm asking for a specific item with specific stars on specific stats. Which then makes the market almost impossible to trade on just because players would be to stingy.
2)Besides not having a standard currency in the game would make it harder for new or less experienced players to get the help they needed from actual trading. Since now they are farming materials that could have been traded for a lot easier on a free market. So would you be insisting on standardizing a currency of some sort? (on this point i get lost because we don't have anyone or anything saying, that's a fair trade. Such as an auction house. Sure you could sell it lower than anyone else, But now your missing out on materials or money. Players don't like to lose money so the Dev's would have to implement a huge bunch of economic balances between new and experienced players.)
3) The community won't be as nice, They ask for a given price and that's just it. plain and simple, there just wouldn't be any sort of bargaining.. even if you were to implement the bot type to set up ranges on what you want to trade things for.
4)Personally I love that there is no money in this game it's just pure mats, just a personal opinion. But it is true that this leads to people being more of "I want materials to better improve myself and all the characters on my acc." instead of "I want all the money in this game so I can buy the next coolest mount when it comes out." (It's kinda the reason why the mounts/costume/pets link to your account. So you have a choice, Do i sell my radiant steed for "X" amount of flux with other players or do i want this mount.
5) To be honest I have only seen bad behavior on the marketplace once. It was because a guy scammed a new player into stealing his cache and chaos chests. Which in return the entire marketplace actually refused to do anything with him and through further investigation with people attempt to "give him a second chance" they were also scammed and everyone that I heard of blacklisted that account that was scamming.
TLDR: I am not very fond of the idea of a trove being anything other than a free marketplace, this gives Dev's and the community amazingly less trouble in the long run. As I'm sure things will change i hope this is an area where people can be smart and honest about things. All in all I would be really disappointed if it ended up like Maplestory's marketplace. These are just my opinions I thought you should consider for changing a great marketplace like this.