This article from the Associated Press covered Simpson's appearance this evening at the convention. It includes the following…
The former football star, who flew to California from his Miami home, said he occasionally appears at memorabilia conventions to sign such things as football helmets, jerseys and lithographs for collectors who pay top dollar. He acknowledged he was being paid for this appearance but declined to discuss financial arrangements. "All the guys do this," he said of his fellow retired athletes. He also suggested he needs the money to pay for college educations for his two youngest children.
Okay, the other article said he was "not getting a penny" and this one says he is being paid for the appearance. Why do I believe the latter?