4. If it was considered beautiful once, it will be considered beautiful again.
This means taste goes in cycles. For the longest time you couldn't give away Elbert Hubbard's Roycroft publications. His entire output bound in limp leather was considered the drek of all drek. Now it’s all the rage. So when you find something odd but out style don’t ask: Is it coming back? Of course it’s coming back, the real question is: When and do I have the time and space to wait?
5. Invest in the 19th century America
My dad thought the 19th century was the great undervalued under-rated era.
So much happened, so much was invented, discovered and explored especially
by Americans from 1800-1899 that it would be impossible to list it all.
But during the 20th century most of the snootier dealers thought the 19th century, especially the late 19th century, was worthless. True, there is an awful lot of junk there, but there is also some spectacular and wonderful stuff and much of this period is still comparatively cheap.
6. If it’s NON FICTION – condition doesn't count
What counts is: Is it all there or mostly all there?
The wisdom of Jock Netzorg goes counter to the prevailing wisdom which says condition is all, and God forbid there should even be the slightest nick to the dust jacket or chip off the spine.
My dad was an expert in buying good books in bad condition, sometimes
falling apart, sometimes without covers, sometimes scribbled or stained or wormed. I assure you in the fullness of time those defects became a lot less important -- especially if the books had wonderful maps or plates or pioneering science, anthropology, or exploration, all highlights of the late 19th century.
Netzorg says: If it’s the real deal, if there aren’t a lot of other ones around, then your ratty copy is better than no copy at all and don’t let anyone else tell you differently. Your job is to describe it well, extol its virtues and price it accordingly.