Rule #1 - disregard trees
Rules #2 through 10 - disregard trees
Check out this web site that only touches the tip of the iceberg regarding published and oft-copied genealogical hoaxes:http://personal.linkline.com/xymox/fraud/hoax.htm
Check out this rich and very deep web site devoted to corrections to Burke's Peerage:http://www.medievalgenealogy.org.uk/cp/vol1.shtml
A lot of the material will refer to items you are not familiar with, but if you study the introductory material it is explained.
Finally, disregard trees. They are no substitute for documentary evidence of the actually-existing kind.