Rare book collecting is usually an operation involving contacts. If you know people who either have books or can put you in touch with someone who does, occasionally you will stumble across really interesting treasures.
One such collector ran into an acquaintance who was in the process of discarding his grandfather's lifelong accumulations of "stuff."
"I just tossed an old bible," said he, "wouldn't have been worth much; couldn't read it. I did see that the printer was Guten-something or other."
"Not Gutenberg?" gasped the collector.
"Yes, that's the guy."
"You idiot! You've thrown away one of the first books ever printed. A copy recently sold at auction for a million dollars!"
"Nah, I don't think this book would have been worth anything close to that much," replied the man. "It was scribbled all over in the margins in German by some guy named Luther ..."
------------------A Final Thought ...
"Cannons and fire-arms are cruel and damnable machines; I believe them to have been the direct suggestion of the Devil. If Adam had seen in a vision the horrible instruments his children were to invent, he would have died of grief."
- Martin Luther (1483–1546), German leader of the Protestant Reformation