For me, part of the reward of breaking up these kinds of estate lots is the search iself... and then the knowledge that I end up helping someone get a desired item for their collection. It's a form of "being of service," ultimately.

I spent 20 years building a stamp collection of my own, and it was entirely self-funding. When we fell on hard times (due to medical bills) that collection was able to fund most of our living expenses, for two years. So that's not too shabby!