There's the big difference between a retail operation and a service operation with pre-payment. One you have already spent cash on the goods and just have to deliver for relatively small cost later, the other the cash is paid and the major expense for the service comes later at the time of delivery. Meaning there could be a year between the cash going in and the expense for that service being realized. With the prepaid option you do get more cash in hand up front before delivery, but that requires good management not to blow it on other stuff as well. It also means the cost of delivery could fluctuate wildly by the time it comes round to being used, where as pricing for held goods and services you can charge on the day of sale what you need to recoup costs. Again all requiring very shrewd management to ensure you don't go negative by the time the service is delivered.