It's a catch 22, we have moved to a 50-75% deposit depending on the client. If that doesn't work you have to make that decision how valuable the client is, you can not finance your clients business and they need to understand that. You can also start charging 1.5% a month interest but I have found that never works. We try to have a long conversation with them explaining the costs of their late payments and work some kind of mutual agreement. Mostly it's about communication, but sometime you need to let a client leave to understand how well they really have it