Providing a Test Server
As with all hosting suppliers, Test servers are never charged for.
For every live server, you should allow the facility for a sandbox test server.
This will make it for anyone who has a live server to be able to test and roll out.
It should be free and will make your package for hosting a very STRONG offer.
Charging customers for a test server is not a good policy. You really need to review this and make it more attractive.

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Kiril commented
Yes, just like Flywheel! They achieve that by adding a username / password to websites, that way public visitors are blocked and only users that have access can visit the websites. As soon as billing is setup for the server, the privacy access is removed and the websites get opened to the public.
Also another great feature that will go great with this one is to transfer billing of a server to another account (and gain an affiliate commission from it), please see this feature request: http://feedback.cloudways.com/forums/203824-service-improvement/suggestions/19188229-transfer-billing-to-another-account-with-affiliat
With these 2 features you can be sure a lot of freelancers and agencies will come running over to Cloudways.