Real autographs are actually quite easy to identify.
If you have a legitimate autograph you should be able to document when and where it was signed or what company actually performed the signing. The highest form of authenticity known today in the autograph world is PSA-DNA because of their strict system of in person authentication. Usually we will have the athelete sign an affidavit with a witness which is available upon request. Yes, we frequently will buy into other signings with reputable companies like Tri Star Productions, The New Score Board Inc., Athletic Promotional Events, and others. We always disclose this in the COA that is issued.