How many times do we see a question with some variation of this here on the Is This Autograph Real forum?
I know others more knowledgeable than me have said this many times, but I'll say it again: A COA means nothing if it does not come from a respected authentication source. Nothing. Zilch. Nada. Niente. Zero. A COA offers no seller protections whatsoever, legal or otherwise.
As a matter of fact, you might say it means less than zero since sellers of non-authentic autographs usually offer a COA since many of the uninformed are so reassured by them.