Also, the only collectibles I ever sell to a vendor are the ones that are selling on the broker for 3c because there's 4 pages of them. For quite a bit of the collectibles, you can get a few gold, and in some cases a few plat.
So if it's a shiny you've already collected, check the broker before you sell it off to a vendor.
Beat me to it. You have a random chance of any collectible available in the zone you saw the shiny whether you've already added it to a collection or not. If you check the broker before you vendor dump you'll see some going for nutso prices; this can mean either rarity or temporary scarcity.
But when there's 11 pages of one collectible? Trash.