There are many lies about search engine optimization - meta tag keyword codes; hidden text; buying links; robot files; Google updates; Bing and Yahoo, yada, yada, yada.
How does one know the truth from a half-truth or a myth?
First, don't believe everything you hear. If an SEO firm (or salesperson) is telling you SEO "stories" the best way to verify is to talk to other SEO firms.
Second, visit and read SEO websites and blogs. Not just one. Read several.
Tweet with and follow SEO experts on Twitter; connect with SEO firms on LinkedIn; participate in the Answers section in LinkedIn (ask questions there; you'll get answers).
Visit and read the Google blog.
Talk to business associates.
Take notes.