If you complete a garrison mission that rewards XP - Item - World of Warcraft on a character level 90-99 with a completely full inventory it will mail the token to you character. You can the go to use either the mobile AH app or https://us.battle.net/wow/en/vault/c.../auction/index to post the token into the AH.
It doesn't seem to be 100% as I completed 2 and only was mailed 1 while still having a full inventory.
This exploit is not too useful, but very strange and may also work with Contract: Ulna Thresher - Item - World of Warcraft allowing you to sell the follower you first get to the opposite faction. Does not work, technically the same followers.
I do NOT take credit for finding this, I saw a mention of it in a thread on The Consortium about seeing garrison resources in the AH and decided to test if it worked with experience and other non-BoP items. You can also see other postings on TUJ and a few wowhead comments, just posting this to inform people of how to do it and test what else can be done.