Odds of Hanging On
It's getting a little tougher to hack it as a rare book dealer. The internet has made it much easier to find rare books. When a collector can just go to Biblio or a similar site and find a lot of what they need, it doesn't bode well for the independent bookseller.
The way to hang on in the rare book dealing biz is to specialize. Become the go-to person for first editions of modern literature, or the industry expert on early-19th century gothic literature. If you've got everything in a certain niche, then the collectors who are fixated on that will come a-knockin'.
You might only make one big sale a year, but if it's a book that goes for $500,000 or more, you'll be making enough for your mom not to tell her friends that you wasted your life.