Well ebay is one place i wouldn't expect to find an invisibility manual ;P But i believe the excerpts said the effect was psychological, and i think
that could be plausible. (then again in the excerpt it says cameras and animals can still see you, yet the ebay version says cameras can not)
Because similar thing is said to be possible using hypnosis (and a person i knew on the web, said he was demonstated the invisibility effect) like
when a person is hypnotised to not see the hypnotist, the hypnotist starts moving objects and the hypnotised person physically actually sees that the
objects are lifted by him, but his mind simply erases the person, and the objects appear to be floating. And indeed a brain is a wonderfull mechanism,
that i believe could accomplish this special effect, if properly told to do so.
However if it's pchychological how do you hypnotize 100+ people crowd without them knowing :/ Large scale NLP maybe ;D