You should get a last name to go with the first name, and then do a search engine search of that name in quotes to see if anyone in any forums are saying good or bad about the person.
You should check to see if John has testimonials from previous customers on his site, and to see if those people are real.
You should read the sales copy on John's website to see if his copy draws your interest to buy.
You should ask John to send you clips of his work.
Myself, I recommend Dan Lok at:
http://www.quickturnmarketing.com/
I have his sales copy in hand, but it is not yet on my site as I am formatting it for final placement into my site. Dan is a bit expensive, but I believe that he is worth every penny.
Bill Platt - Owner
http://thePhantomWriters.com