Earlier quoted context omitted.
I think this is explicitly forbidden by app store rules. It is definitely the case for the iOS app store anyway.
You could create two versions, one crippled for the app store and another that you actively market. There is no point giving Apple 30% if you are finding the customers yourself.
You are allowed to make the same version available elsewhere and pocket the margins.
This is what BBEdit has been doing for many years for example.