It’s obviously a leap of faith when spending any real money on an autograph, which is why I gravitate toward signed checks, official documents, etc. However, I have a HUGE amount of baseballs signed by world leaders, musicians, actors, criminals, etc. And I’m fine with them because I never paid for any of them — meaning I know the provenance of each one, having gotten them signed myself or receiving them from people who had the obvious ability to get them signed. And these are some valuable balls. Because of the expense, I’d really need some good proof before spending 5-6 figures on an autograph. Paul (T206 Collector) does a great job/massive effort of tracking down the provenance of many signed cards in his collection and website. I’m always amazed that the auction houses selling so many valuable, signed vintage cards each month rely solely on the slab for evidence of authenticity instead of tracking down any provenance. I suppose they don’t have to, due to the card being slabbed. Until that changes, this area of the hobby is just very risky.
Here's Queen Elizabeth and King Charles: