This compilation catalogues historical and accomplished makers—a helpful guide in determining the value and import of an instrument. I imagine this would be helpful when doing appraisals. Identifying an instrument to determine it's monetary value can be tricky because labels are often misleading or lacking much identifying information. But, if you at least have the maker's name you could look it up in this book and see if he/she is listed.
Apparently this book is most relevant through the 1950s/1960s or so. It's been in print beyond that, but it's not up to date with more modern makers.