Outsource Your Invoice and Get Paid Immediately (outvoicer.com)

This is nothing more than a modern debt-collection agency.

That may not be an entirely bad thing, though. I can just see it getting out of hand if this is not done correctly.

They're not as bad as the loan sharks at pay day money shops, but 4% commission is still a substantial chunk.

I've found it really effective to invent an in-house, debt collection agent. Usually named Boris, Thor or Moose. He contacts late clients directly from our billing dept, and is a little more insistent than I'd been up to that point. Whether the delinquent client takes him more seriously, or just finds the whole process humorous, I don't know, but it works.