When you quest and it says you have an item in a shop you have in a shop. Maybe it should also show if you have it in your vault and give to the choice to move it, just like if you had it in your inv. It'll make questing easier and cheaper.

There's no need for this since you can just hover over the item and click "account search" which will show if you have the item anywhere on your account, including your vault.

Sure there is because what lazyanon suggested is fewer clicks than that, and buying a new copy is faster than currently getting it out of your vault

Sounds like a good idea to me.. is lazy