The sole most important thing to be focused on while buying autographed memorabilia is the product authentication. Unfortunately in this industry there are a lot of faked items-- similar to knockoff products. However, there are ways to be sure that you will only receive authentic memorabilia.
Buy From Reputable Companies
In this industry, there are a handful of reputable companies that authenticate item to give the buyer a peace of mind. These companies include James Spence (JSA), Beckett, PSA/DNA, Fanatics, Steiner, Tristar, and Upper Deck. While some of these companies provide authentication on their own items, some of them provide authentication on other items.
Difference between Witness Protected and Third Party
JSA, Beckett, and PSA/DNA all have authenticators that personally witness an item signed at a signing. These items will have a certificate of authenticity with them saying that the item was signed in the presence of a company representative. These companies will also authenticate items sent in to them and they will look at factors such as hand stroke, the autograph, databases of the autograph, and other things to determine if the autograph is authentic.
Ultimately, the best way to buy authentic memorabilia is to buy from reputable companies. These companies will not risk their name and reputation by authenticating fake autographs.