How do I switch an item from one client to another?

If you decide that you need to change the client associated with an item, follow the below steps.

Does the item currently appear on any documents (purchase order, proposal, invoice)?

If not:
Select the item, head into the "edit item" screen, and select a new client/project, as well as shipping destination. 
If so:
If the item does appear on a document, you'll need to first remove it from whichever proposal/invoice it exists on. Please note that if this is the only item on that document, removing the item will void the document.
Select the item and head into the edit item screen. Make sure there are no payments applied to the item. If a payment has been applied, you'll need to remove it.
Once you're on the edit item screen, there are a few fields you'll need to clear before you can reassign the item: Proposal # (or Invoice #), and Client Status.
Hover over each of those fields until a red x shows up, then click it to clear. Once you've done this and saved the item, it should successfully be reassigned to a new client of your choosing.