People talk about Global Auction Houses and people rarely agree, but here's what I'm thinking...Guild Stores...for the already existing Guilds within the game. Fighters Guild, Mages Guild...and possibly even the Undaunted.
To sell in the Guild Store, you'd have to reach Rank 10 of their respective skill line AND complete their main stories with any of your characters.
They would function exactly the same as existing Guild Stores, but the Store itself will be accessible at any of their Guild Halls (Enclave in the Undaunted's case). The stores would always be in the same place, no need to worry about switching traders every other week.
As for limitations, players could only have 10 listings in each store. This would allow players who weren't part of a trading guild to still sell some stuff on the side, while at the same time players who are actually part of a trading guild can sell more stuff due to the higher number of listings they can have at once.
The developers could even add special items to these guild stores themselves when they feel like mixing things up.
Guildmaster of Spectral Liberty - Xbox One - European Megaserver