Other than that, as I already mentioned, The Blueprint by Ryan Stewart is probably the only thing you need to buy if you want to scale an SEO agency.

That said, not ALL free stuff is useless, I mentioned I read a ton of books and listen to a lot of podcasts so here’s a nice list to begin with (most of these are not SEO related, I prefer to keep my reading and listening for self improvement/business stuff)

Author's Bio: