
Things to consider:
1. Important authors: While I have most of the important texts by Child, Beard, Crocker, Claiborne and others, I don't have all of them. Take a chance, roll the dice--you could come out on top.
2. Illustrations: As an incredibly visual person, I'm oftern drawn more to the photographs or illustrations than text. Initially at least. Look for something specifically indicative of a period. I have a Jell-O cookbook from the 1930s which has the most adorable little deco illustrations of wealthy-looking deco women serving Jell-O. Or their maids serving it. Will I ever make any of those recipes? No, but I do like looking at the pictures.
3. Condition: If it's falling apart, it's probably been loved enough.
4. Hidden secrets: There is nothing I enjoy more than acquiring a cookbook and then finding scraps of recipes inside. Or notes. Or references to other recipes. Those recipe file books? Those are the absolute best.