Glory
We've never actually heard anybody describe a career in rare book dealing as "glorious," but we figure there has to be some glory involved if you're into this kind of thing.
Let's say a collector has been searching her whole life for a copy of On the Origin of Species signed by Darwin, and you're the dealer who just so happens to find one at some old lady's yard sale. When you place that book in that collector's hands and see the ecstatic look on her face, that'll surely make you feel pretty good.
Of course, the millions of dollars that'll flow into your bank account as a result will make you feel pretty good too. You don't even have to be into old books to see the glory in that.