I'll analyze the auction house ("broker") feature because -- to say it diplomatically -- there's a reason SW:TOR now has to patch up their "auction house" in their next few patches (if they haven't already).
Use cases for the broker:
- Player wants to sell an item they possess.
- Player wants to purchase an item they need.
My expectation is for production to understand and own the implications of the use cases in the context of their particular games. Here, we'll look at the first case generally, avoiding going too far into game-specific minutiae.
- Player travels to the broker NPC to interact with it.
- The interaction brings up some UI, but the player doesn't really care because...
- ... the player right-clicks on their item that they want to sell. The UI populates the search field with their right-clicked item.
- The user presses Enter or clicks the Search button to see all current listings.
- The player now knows what their item is worth. This is an intention!
Compare this against (disclaimer: what I remember of) the equivalent SW:TOR Galactic Market use case.
- Player travels to the Galactic Market terminal to interact with it.
- The interaction brings up a UI.
- The player looks at the drop-down labeled "Required" to understand the drop-down selections.
- The player chooses the drop-down selection that seems most appropriate for the item.
- The player hits search that returns the listings of that drop-down categorization at that time -- but to enable the Search textbox.
- The player types the name of their item into the Search textbox.
- The player presses Search to search for listings that correspond to their item.
- If no listings are found, the player might go back to step 3 to make a different guess at categorization. If listings are found, the player now knows what their item was worth at the time they searched for the categorization*!