How often have we seen this question asked...this is the most comprehensive book that I've seen written.
http://www.huffingtonpost.com/daniel-grant/a-book-for-art-dealers-al_b_10800300.html
https://www.amazon.com/Selling-Contemporary-Art-Navigate-Evolving/dp/1621534626/ref=sr_1_1?s=books&ie=UTF8&qid=1467664658&sr=1-1&keywords=selling+contemporary+art
http://www.huffingtonpost.com/daniel-grant/a-book-for-art-dealers-al_b_10800300.html
https://www.amazon.com/Selling-Contemporary-Art-Navigate-Evolving/dp/1621534626/ref=sr_1_1?s=books&ie=UTF8&qid=1467664658&sr=1-1&keywords=selling+contemporary+art