Why not add a trash bin upgrade to guild halls? It's basically just a storage that auto-deletes item in it older than 24h. If there's something you don't need but you think it could be of value to others in guild, maybe that's better than just merchanting it.
There's a similar request of adding a Guild Bank. Although this is distant related, this is a much easier solution. Devs don't have to consider implementing security issues, like who can access what, if new players can just clean out an entire guild's storage etc. Since this is a trash bin, it's free for all who can access it, including guests and alliance members.
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