This was the most helpful response for me. I was looking to zero out old uncollectable tenant balances from years ago. Since I use cash accounting, I knew that writing them off as a bad debt was incorrect, but I didn't think to use a credit memo. That did the trick. I would add that it was important to use the same income account as the charge you want to cancel out, so I needed to create multiple credit memos, since there were some outstanding balances for different things such as rent, late fees, and cleaning charges. After creating the credit memos, it is necessary to go in and Receive Payment and apply the credit to the outstanding invoice. Thank you for this tip!