@Heather1051 Cost of Goods Sold is anything which relates directly to the booking itself. In other words, any costs you incur for preparing the rental for a booking.
Mortgage, utilities, and other items generally paid by the month instead of per booking would generally be considered overhead, not cost of goods.
If a property manager is paid monthly, it would be overhead. If a cleaning service is paid per booking, it is cost of goods sold.