Whiy is an autograph on a card worth 10X

[UKCardGuy]

Originally Posted by egri

Set collectors have something to do with it. If I want a signed 8x10 of Willie Mays batting in a NY Giants uniform, there’s plenty out there that fit those criteria, and the prices reflect that. But if I’m building a 1957 Topps set, it has to be that one, I can’t use a different year or brand instead. So when one does come up, I need to bid accordingly, since it’s a very specific thing I’m after and I’m competing with every other set builder for it as well. There’s also a time crunch for players who died young; Harry Agganis signatures are relatively plentiful, as he had a successful career at BU before turning pro (there are several on eBay right now) but he only had a couple of months to sign his 1955 Topps card. A cut signature might go for several hundred dollars, while two copies of his Topps card sold this spring for $15,000 and $27,000.

Thanks guys. I get that for some scenarios (e.g. Agganis 55T) the rarity commands a premium. But other times, it seems to me that there's a multiplier on an autographed card that sometimes defies logic.

I expected that autographed set collectors were a pretty niche group. But I've probably massively misunderstood the market.

Excepting the rarities like 55T Agganis, is there a general rule of thumb about the value of an autographed card vs an autographed photo?