Man, this guy has a bass "signed" by all 4 Beatles for $25k. I feel bad for whoever buys that.
Yup. This is why autograph collecting is so precarious. It's expensive if you need or want to buy something, and there's tremendous uncertainty. Basically, all of it is personally questionable unless:
-You had the item signed in-person and primarily for your own fandom and collection
-You bought the item from some kind of widely known, verifiable, and celebrity supported promotion (like PledgeMusic or directly from a Band's website promotion)
I also think that this is something that the modern trading card hobby has done exceptionally well with. When they are randomly inserting signed cards into packs, these are big organizations who are putting their entire reputation on the line. And so, generally you know that these cards are authentic, with announced signing limits, hologram verification, high production value, etc. Most people will be comfortable buying those cards for the signatures 20 years from now if they decided to.