There are, four axes that determine how well your art will sell.
If you're weak in one, you've got to be stronger in the others.
They are:
1. Price Level
2. Uniqueness of niche
3. Mastery of craft
4. Skill in Marketing
Sales Axis 1: Price of Art
A lower is better when you are first starting and for most artists, assuming you don't go so low that people wonder what is wrong with the art.
If you reach a point where your art becomes a sought-after Veblen good, then higher is better.
Sales Axis 2: Uniqueness of your art's niche
If you create something that nobody else does that is a powerful sales tool. An example is Jeff Koons with his "balloon sculptures" orGeorge Rodrique who painted his famous "Blue Dog."
Sales Axis 3: Mastery of Craft
If you are Michaelangelo great at your craft, you will almost always find a buyer. This is the art equivalent of "Be so good they can't ignore you."
Sales Axis 4: Skill in Marketing
If you are just a fantastic promoter or marketer you can overcome weakness in the other areas. Think how well Thomas Kinkade did in his heyday, even though there are much stronger painters than him.
To consistently sell art you probably have to be really good at one of these 4 axes and at least average in the other three. You might be able to be below average in one if you're exceptional at one.
Ex: If you're as good as Michaelangelo it's probably ok to suck at marketing
Most of my lastest thoughts (like this newsletter) are posted to Twitter these days. If you'd like my thoughts on art marketing I highly suggest you follow me there.