Help me sell SEO ideas to my customers

As a merchant services broker. I speak with small to medium enterprises buisness owners all day every day. I save them from €500 to €5000 yearly on their merchant services bills. I want to have conversations with them about reinvesting their money in SEO projects, I need an expert to consult with. I would ask you to analyze their website/buisness and suggest improvements, and carry out necessary marketing maintenance or new projects.