Currently, these can only be fetched via actually viewing your listings. I was hoping it'd be possible to reference them outside of that in a manner similar to the current GetItemLink:
GetItemLink(number bagId, number slotIndex, number LinkStyle linkStyle)
GetGuildListing(number guildId, number slotIndex, number LinkStyle linkStyle)
It would return item link, quantity, listed price.
Or, to reduce the DB queries, it could simply be:
which would pull all of your listings for that guild and then you'd have to sort through the table it returned.
My planned implementations for it would be for my Wealth Evaluator addon (which currently requires you view each of your listing pages) as well as allowing you to pull up your guild listings on demand when away from a bank so that if someone asks for an item, you can check if you have one listed.