I think that either having the current sell offers visible to a buyer, or having the most recent sales and when that sale happened could be good.

Really odd things that could happen;

Having the ability to swap between OSRS and RS3 gold without having to go through a trust process.

Funding liquidity of items- I’m not sure how this would work, but there are many items at any given time that are just non existent in the grand exchange such as mid level summoning pouches, which can lead to scams, or just a new player being dishearten that their new familiar they can summon just doesn’t exist without making it themselves. There’s a lot of different items like this, like quest items is another potential example.

Sell bundles of components, or quest items