Authentication

[kriwill-3412]

So I had an item sent to authenticator and buyer says doesn’t seem authentic ? I’m new to this so My question is how do I as a seller find out what makes it not authentic? I would think I would get something written describing what was wrong with it?

thank you to anyone who can answer this for me

[comics-scifi-collectibles]

@kriwill-3412   Did it pass the authentication by eBay?  Then the buyer should not be able to say it's not authentic.  

[kriwill-3412]

They said it did not but how do they determine that? How do I found out if it authentic or not?