I've just started working at a real estate company. Some of our customers make a small down payment to reserve a unit and occasionally take a long time (~2-3 months) until they bring the rest of the money and close the deal. Some customers give it a second thought and abandon the deal, hence they request back their down payment.
I feel like there is a considerable opportunity cost in reserving a unit for that long, given that I might be able to sell it for cash the next day. There are also accumulating expenses like salaries and operations costs in closing the deal.
How do I calculate the opportunity cost caused by the delay in closing the deal?