Traditional SEO retainers usually cap out at 30 percent margins, but...

https://dibz.me/blog/why-a-handful-of-european-seo-agencies-stopped-being-agencies-and-1138

Traditional SEO retainers usually cap out at 30 percent margins, but productizing your internal scripts can get you past 70 percent. Treat your agency like a lab to build tools that solve real problems, then sell that software as a scalable product.