For autographs (not commenting on game used), in person signing companies are very reliable, as the signings were done with witness and the players are generally under contract to sign. These companies include Steiner, TriStar, Mounted Memories, UDA (and others). The player's hologram next to the signature is a good sign of authenticity. The MLB hologram is also a strong indication of authenticity, as these signings are also done with witness. PSA/DNA and JSA are generally reliable 'after the fact' judgers, though aren't perfect. They don't witness the signing, but are judging later. GAI letters where Mike Gutierrez is listed as expert are reliable, as he's top notch. He left the company early on, so later LOAs won't have his name.