I googled Guy Schenker, D.C. and found some interesting commentary on some of the products he pushes and in particular, Nutri-Spec:
NUTRI-SPEC Testing Is Pseudoscientific Nonsense
Stephen Barrett, M.D.
... "Simply put, NUTRI-SPEC is pseudoscientific nonsense. If you encounter a practitioner who uses it, please ask your state attorney general to investigate."
In other words... it's reader beware. There is a fortune to be made on the internet pushing and peddling products.
Just found this forum, interesting stuff and it seems like a good resource.
I found this post while Googling through some material, and wanted to make an alternate statement. Sorry to bump this up, though it's only a couple weeks old, so not so bad.

I don't put much weight to Barrett's opinions. He is a very bitter person, who obviously pays heavily for his advertising, since ChiroBase and his other domains come up in the top of many searches that contain things he opposes. And that includes just about anything non-allopathic.
I don't think he's useless, and haven't met him in person, so I won't slander him... But I will say that he's been laughed out of court for his cases on a few occasions, for having no actual facts to back his cases, just a lot of slander. Last I heard, he was moving from PA to NC. Maybe to try again, I've no idea...
I agree that internet research has to be taken with a grain of salt, but there's a lot of VERY respectable MDs/DCs/whatever who use programs like Nutri-Spec or others. So it's not all hocus-pocus, internet-only jabber.
Yes this is my first post, and yes I know that newbies are often ignored. But I just wanted to chime in, on this one. If you want a little objectivity to Barrett, one site to check out is www.quackpotwatch.org