Add the possibility for us agencies to resell clients accounts with our logo and custom domain.
Ie: Basic package of let's say 50usd for 2 clients and 10 USD monthly per new clients while offering 14 days trials to our users.
For each trial that convert to a sale, you charge us 10 USD and we charge the customer 30 USD so we have a bit of extra money to hunt for new customers(advertising).
You would sell more via many agencies looking for customers on your behalf.
Some of your competitors are already doing it but asks for a 12 months payment in advance which makes no sense for a small agency as pay as you grow means that you only pay when you make a profit and not before.