The Tax Book, or Quickfinder, are both good basic research sources.  One of them should be in your library to research such questions.

Even google has tons of info:

https://search.yahoo.com/yhs/search?hspart=avg&hsimp=yhs-securebrowser&type=8153&param1=e0f50a024ae1...86.0.6536.113&param4=17|US|2.5.127|1.23.0.675&p=sale+of+client+list+tax+treatment