Convincing a client you can deliver an agency as a sole proprietor is difficult but incredibly valuable.
Laura Elizabeth of Client-Portal.io discusses how she does it, and the tools and techniques other freelancers can use to elevate their authority with clients.
Client Portal: https://client-portal.io/
Laura's article on onboarding clients: https://doubleyourfreelancing.com/onboarding/
Lauren's Twitter: https://twitter.com/laurium