[Porsche-O-Phile]

You could always demand a percentage as a retainer/deposit. That's how we do most of our contracts - X% to get going, Y% at some milestone (60% completion, usually) and the balance upon completion. You could implement a policy like that for all but your "preferred" customers (who get standard 100% invoicing) and tell everyone that you're doing this (and guess what, you're not a "preferred" customer, in not so many words). It's a subtle way of telling them, "if you're going to play these games with our billing, we're going to make it harder on you, but not to the extent we're willing to throw away the contract". Basically call their bluff. Or simply tell them they're no longer eligible for the discount at all.

My firm pays EVERYTHING on receipt. One thing I absolutely believe in (especially in business) is "pay your bills on time". I don't care if some bean-counter tells me we're losing $100 a year in lost interest gained by holding the funds or whatever, clients, customers, consultants and other professionals recognize it and appreciate it. I believe it comes back to us in the form of healthier business relationships and more work.

One of our former clients used to have a standing "120 day clock" for all invoices. Can you believe that schit? FOUR MONTHS to even CONSIDER getting paid. A small business (even many medium ones) simply can't operate running continuous deficits or "gap" measures like that. Glad to have better clients now.