one of my competitor site returns the following info when I check it out by SEO tools: Keyword density: 4.50 keyword found: 7 [according to my desire keyword] But when I manually review that site I found only 1 keyword!!! whats going on? Is this site use 'BlckHat SEO'??? or something else?
They might be put those keywords on below sections please check it once. Title META Description META Keyword
keywords in metatags and keyword will not visible in the website for your eyes and it helps a lot in SERP.
Difficult to say... Does your tool count meta data? Also, view the page source, and make sure they have no hidden text - using text colour the same as their background colour etc, etc etc