If you're considering managing your client's social media site you need to watch this first. Facebook has a new process in place that requires business verification prior to even requesting access to your client's page.
Once you have your verification, you can manage the client's page via GHL and charge a monthly fee to manage.
If you're new start with a trial offer, it reduced the barrier to entry. Once you prove yourself over a few weeks negotiate a better deal from a stronger position. You already have access, and the client is seeing visual results on their page, it's a much easier position to negotiate a deal.