This was not a item from ebay, I bought it from another collector. There are few autos that I can tell if there likely authentic or not such as Wright or Beltran since I deal with there autos a lot but I would still not advise someone to buy an item on my opinion. In either case this was a space item, a new area I recently started collecting in. If you feel you can authenticate every auto you buy that's great but to me 3rd party authentication is very important, so long as they are a reputable company. Also having someone whose job is to study autos look at your item isn't speculation. While getting my physics degree I took a class in handwriting analysis and I can tell you if done properly it is a true science. If anything forming the foundation of an autos authentication based an what the seller tells you would greatly depend on your trust of the person and is still, without evidence, conjecture at best. I understand the only way to be 100% sure is to see every item in your collection signed in person but unless I win the lottery tomorrow its not possible for me to fly to every autograph event. On the same note since I have a limited amount of money I can spend on my hobby I will not buy an item if I can not be almost certain it is authentic. There is to many authentic items out there to have something on your wall with questionable authenticate.

Back to my original questions do you think it would be different since the seller said he guaranteed it would pass authentication?