Authenticating Autographed Items?

Autographsamerica.com sold my adult children two Grateful Dead lps with the band's signature on both. Anyone know how legit autographsamerica.com is? While I'm touched by my chidren's thoughtfulness is selecting such a cool gift for their "Baby-Boomer Dead Head Father", I have an uneasy feeling they may have been ripped off. Not being a crime specialist I'm seeing too much variation in signatures among the other Grateful Dead items at their web site, and between my own autographed gifts. What do you think? Are they legit? Any Dead Heads out there able to compare their own signed items with what's on Autographsamerica's web page? Similarly, how do you know those autographed items you have framed and displayed are signed by the artists you admire? Do seller's "certificates of authenticity" have any validity? - Restless in San Francisco