I can't work out if one of these has happened in living memory .... I am thinking of a live auction with an auctioneer (DM?)and an audience. Items could be either good stuff that players are trying to sell, weird or unique items the DMs want to introduce into the game, or perhaps even services that others want to make available (crafting etc).

Yes it may well be complicated, but it might get some money moving about rather than languishing in the accounts of the hoarders!

And most importantly its one of those mass RP events where we all learn a bit more about each others characters .... particularly how rich they are!

This is not only possible, but also has been done to great success. One might want to skip all mundane items, as it takes a hell lot of time if you bid on all of those.

I know it was done on The-server-which-I-will-not-now-name to at least fair success. It was player-run there, usually by a noble house.

There have been auctions by DMs in the past, the tiefling and duergar ones most specifically, most of which failed due to people not bidding because the items didn't have some kewl loot effectz.

There have definitely been some cool ones in the past, Player and DM-run. In the case of the latter, they're done at our discretion- From inter-planar bazaars to Fort Mur slave auctions.