Anyone in the service business without a c.o.d. policy ought to have his head examined.
Sending out a bill for your services entails numerous disadvantages. For instance:
1. Most obviously, the money sits in the customer's checking account rather than your own. You lose interest on that money. You also invite cash flow problems that could make it hard to meet a payroll or take supply house discounts or impress a banker when needed. As soon as you perform a service, you are entitled to money in return for that service. Neither the law nor business ethics requires you to give the customer 30 days to pay.