I don't know that there is a set answer to this. Regardless of the account you use, it is an overhead of doing business. Most sources I've seen indicate that lost sales are not found in the accounting system -- they are oppportunity costs. So I would suspect they should be treated as administrative costs until the time of the sale when they are transferred to another account to track the cost of the same. That should enable you to also compare the cost of sales made vs. sales lost. I recommend you consult your accounting professional for local regulations and best practices.