Baseball memorabilia follows the same formula of economics ... supply and demand.
I owned a trading card/memorabilia store for 15 yrs.
Assuming the autograph(s) are considered valid, legible on a piece in worthy condition the single signature is relatively easy to determine the range of value. The value for that player's signature is pretty much known based on how popular the player is and how plentiful is the autograph.
Now, for the multiple autograph piece. If one has, say, a baseball signed by Ruth and Gehrig, the value should be considered greater than the sum of their autograph alone as the supply would be diminished and the demand increased by how the 2 team mates played such a significant role in baseball history.
Now, let's say someone had a ball signed by Tinker, Evers, Chance and Heinie Zimmerman. The ball loses some of the market share demand because Zimmerman is on it as most people have no idea who he was even though he was on the 1908 Cub team which won it's 2nd consecutive WS that yr.
If the Zim autograph is needed to verify the yr., it could be helpful.
Sometimes people would show up w/ an expensive card that was autographed. I would explain to the person the card is more valuable to some people, but fewer people would want it as they may consider the ink ruined the intrinsic value of the card.
The most valuable item would be a single signature on a bat or a ball (doesn't matter) by a hall of fame player whereas the the bat or ball was proven to be the item he used or hit in an important game.
For instance. If you had a ball that was homered by Babe Ruth during his 60-home-run season in 1927, and could absolutely prove it, then you'd have something valuable.
For a multiple signed item it depends who the other autographs are from.
A ball signed by Derek Jeter only is more valuable than one signed by Jeter and Alfonso Soriano. It's also better if the single signature is on the 'sweet spots' of the ball and the bat..
A multiple signed item is especially more valuable if it has a theme, i.e., 3,000 Hit Club, 500 HR Club, 300 Win Club.
Depends upon:
a. condition (of both the item and the graph(s))
b. specific signature(s) (and I'm presuming different player signatures, not different sigs of the same player)
c. if multiple autographs, is there a recognizable theme? (Say, an All-Star delegation or a championship team, not a bunch'a guys from a random day in spring training. Hall of Famers always carry the day here.)
d. if multiple graphs, are there key names among them? HoFers, award winners, All-Stars, fan favorites, particularly rare autographs?
Multiply-signed items are more elusive to assess, but if the set has special appeal based upon a theme and key names, it will probably command more than a single item, given comparable quality. But the single-signed item is probably easier/quicker to sell because the buyer knows exactly what he is getting, and may only be interested in that one name.
If you have Warren Spahn on a ball with the 1957 World Series champion Milwaukee Braves, with Aaron and Mathews and Adcock and Crandall, that ball will sell, easily.
If you have Warren Spahn on a ball with the disastrous (albeit entertaining) 1965 New York Mets, that item will have less appeal to most buyers, though if you lucked out and had Yogi Berra on it as well that would help.
If I have an autographed item, say a ball or a bat, is the item likely more valuable if it has a single autograph, or multiple autographs?
