Mark B. Ledenbach's vintage Halloween collectibles blog.

Vintage Halloween Bridge Tally Card 1920’s Excellent Condition

This is a good example of what I mean when I refer to SGV, or sustainable guide value. This same seller listed an identical item that ended on August 14th for $82.77. The second identical listing ended on August 22nd for $37.99. If a seller were to list another one in the near future the price should be even lower. At some point, the "bedrock" value of the item would be established at, let's say, $25. That latter figure would then be the SGV. The values cited in my reference are for an item's SGV. 

09/02 Update: The same seller sold a third identical item on September 1st for $53, an unexpected result. The same seller listed a fourth identical item today. That selling price should be conclusive in establishing an SGV.