Check all the autographs the sellers have sold, think about how they continue to sell the same signed autographs over and over again.
To get one fully signed shirt can take a long time let alone from different teams up and down the country.
Some continually sell signed England shirts just consider the travelling involved to all the clubs to get just one shirt signed. And then there's a Pele or George Best shirt - believe me getting a pele signed shirt is like winning the lottery - do not be fooled.
Due to so may fakes a lot of celebrities will not sign autographs and security is much tighter than a few years ago. If they have too many of the top names it should set off alarm bells.
If the seller hides his feedback this can also mean he doesn't want you to see they are selling the same shirts over and over again which raises suspicions.
COA's mean very little as anyone with a printer can make these for nothing.
Photo's can be a good way of proving authenticity but be aware people who use pictures readily available online and use them to prove there product, make sure the picture shows them signing the exact same piece that your purchasing and the signature is in the correct place. If they use a picture of someone signing a different product than your bidding on or just a random photo of a celebrity in a car, there's a very high chance its fake.
Price can be a good indication also is someone is willing to sell there shirts at rock bottom prices over and over think to yourself how on earth can they be profitable after all the traveling expenses they must incur.
Feedback - If they have great feedback this doesn'’t make there autographs genuine, it just means they get the product out to you in a good condition, it has nothing to do with authenticity.