It's worth noting that no amount of analysis and research is likely to change the cold hard facts: that there are more individual humans trying to sell Fine Art Photographic Prints than there are individual humans wiling to buy them, at any price. I think this may be literally true.
This is gonna push the prices downwards.
Which means that in order to sell prints for more than a few cents, you've got to skirt around the realities of the supply and demand curves somehow. The tourist-targeted hard sell gallery is a good example of this. Essentially, you lie about both supply and demand, and use various psychological tricks to produce an impulse buy.