its possible to share the Achievement My Sack is “Gigantique” with a little trick.
The tooltip says you have to equip it and from that point it will be soulbound, but you haven’t.
Buy the bag. This will give no Achievement to you:
now here is the exploit. If your Backpack is full, the game thinks that you equip the bag, when its stored in one of the 4 aditional bags.
trade it back
gratz! repeat it as often you want!
While you can just share the Achievement with friends and guild, it also opens you the opportunity to refund through an GM or sell the Achievement to other people for maybe 20-50g. When doing so don’t forget to hold a pledge, to be sure you get your Bag back.