When you click to "return transaction", it brings up a search box. If you click the button to "search for items", it takes you to the items list, but when you find the item to return, it tries to add it to the transaction as a purchase and doesn't bring it up as a refund. If you have the exact lookup code, you can put it in the initial search box and click on the search icon, but I'm not clear on the purpose of the item search button on the bottom right.