For new clients, I require 25 to 50% of the total project fee before starting. I submit an invoice for the balance due at the end of the project and require payment within 30 days of the invoice date.
If any client is 30 days past due, all current work stops, transfer of copyright is withheld, and the client is dropped from my client list. I believe in mutual respect between myself and my clients. I deliver projects on time and I expect to be paid on time. Failure to pay on time is a deal breaker.