2. I want to sell ERPNext Service to my customers. How can I do that?
Before you sell anything to anyone, you must be completely convinced that it is the right tool for you to promote. After all, it is your reputation at stake. Before you sell any ERPNext service, we recommend that you evaluate ERPNext very minutely yourself and the best way to do it is self-implementation. Start using ERPNext for billing, customer support, CRM, quoting your customers. Even if you don't wish to use it in production, use it as a test. Once, and if, you are convinced of the application, you should demo it to your customers. Nothing sells better than confidence, so its best to be confident before you sell.
Disclosure: We use ERPNext extensively in our own organization too!