In addition to the wonderful answers already provided. I've found that my clients will pay based on how I allow them to pay. There have been times when I've also been concerned about being to forceful in a good way, to get paid sooner verses later. However, what I'm also realizing is that,  if I'm not assertive, then someone of my clients will pay when they remember to pay. Generally, After another email with my follow up invoice which for some is 30 days later. We just can't be shy about asking for the payment we agreed too. My mentor reminds me that If we're in business and not making any money, we're going out of business. Being paid sooner is critical to the life blood of the business. Cash has to flow. If your client and my client had an issue, they wouldn't hesistate telling us or just switching to a new service provider. We certainly can't be so attached to clients whose payment process drives us out of business. Our business is our responsibility.