Consistency, quality and the ability to connect with a specific audience.
Art Buyers, or Buyers of Art, are of infinite variety, and ever changing, connecting with the right group is paramount. If you want to reach specific buyers, you have to produce specific artwork that "speaks" to those buyers.
You have to give something to your audience, a reason to want your art, a reason to care about you and what you create.
Developing a style that resonates with the general public is tricky, developing a niche is a lot easier.
-YoPedro
Twitter@YoPedro