Where do"SEO Companies"learn how to do what they do?

[kokoarteest]

I am a web designer and am learning about search engine optomization. My question isn't how to optomize a site. it is - how do you learn what"SEO Companies"like the ones that claim they can get you to the top of google search or yahoo search know how to get a site to the top? They must learn how to do that somewhere or do they just buy like bulk rankings from yahoo or google and pay with a markup to you to make your site show up first?