Search engine optimization is a critical part of your web presents.
There are many companies offering SEO for websites. Some are more capable then others, but in the end clean code and fast loading pages counts for much.
Over the years I have watched how SEO sellers will do things like setting up multiple fake websites loaded with links to their customers plus many other tricks that no longer work.
Every year google modified their algorithms to ignore much of the cheating tricks used by some SEO providers.
In my opinion to understand SEO you must think like google and other search engine providers.
They want their users to get a search result that truly reflects their search query.