A couple of suggestions.

[T0M]

Allow // to work as well as ::yell

If possible, allow people to offer up buy offers on items in the trading post, as well as sale offers.

Change the colour of yells to something that isn't black, to offset it from normal game dialog.

Make staff chat bypass public chat hide/off.

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A rather controversial one - have a rank of sorts, for a select few players, "middleman", these would be players trusted to hold pots during a gamble either for their own games, or holding for 2 others who are playing.
These players, might be able to require a fee (upfront) for their services.

This has been tried .. elsewhere, and proved to be effective at reducing scams by a rather huge portion.

[Vanilla]

I like the idea of staff being able to bypass chat being off/hide. 

Love the idea of being able to list items you want to buy in trade post also, though I feel it would be difficult. 

Some good ideas though 🙂 All trusted middlemen are usually found on forums with vouches or you could also ask a staff member 🙂