This always worked for me in all the years I was a builder:
50% down on all orders, no exceptions, even government!
50% cod on completion (not one day, not 10 days, you just have to call ahead your client and warned them that an installation or delivery is scheduled and that they need to have payment ready)
remember if a client is not willing to pay a deposit, may not be willing to pay at all.
if you absolutely need to give someone an account, ask for the first 3 purchases pre-paid
5% discount on pre-paid orders worked great as well
Steve
http://www.signestimators.com/