My good friend, Tony Moffitt on his blog
http://tonymoffitt.blogspot.com/ makes some very good points about ways artists should follow to improve their chances to sell their work.
As with every investment, if you want to be successful when investing in art, invest in someone who looks desperate an cheap.
Look for people with plenty of art and even more advertising on their blogs.
Desperate means that person is putting a lot of effort into selling his work.
Cheap means you are in for a bargain.
These are people where you should buy in bulk. The more you buy from them, the more other people start seeing them take off and the ball starts rolling.
With people that look confident and expensive, no such luck.