Gaia Online's trading system had a lot of freedom, where 99.9% of content can be traded (soulbound items are untrade-able, but they are usually only items that people don't even care about). The items could be traded from their inventory, items can be gifted, and items can be auctioned off. I don't really go on that site much anymore, but I'm wondering what Gaia Online staff did to make this system work out for them. It would be interesting insight for the Rumble Fighter trading system discussion
Or better yet, just create a company, get a really good dev team together. have them work on a new game with all of the positives of Rumble Fighter, The Sacred Scroll system for one it is so good, and the EXO system is really fun. If i had the amount of money it would take to do such a thing i dam well would do!
It will be similar to Warframe's trade system. Look it up. They only selling the rare items. The buyers had to using the cash to buy them in the trade system. It is only make sense if they get duplicates, they would selling them that the player is able to obtain but with their greed action the price would be ridiculous highly price. If nimonix copy warframe's trade system there chance they would make alot of profits. I dont care about the dam carats to RC or RC to carats items. Only I cared about is rare to RC.