Selling work that has only been viewed by the buyer online is a hard sell. So much of the fineness of a print is lost on the screen. I think that the work for sale has to either be priced at a price low enough where the buyer feels that there's little to risk, or the work has to be sold by an established artist who can be googled to check their "credibility".
You have to put yourself in the place of the buyer. Whose work, or what work would you feel comfortable buying based solely on a jpeg? How much are you willing to risk in terms of a purchase price? Would you google the photographer and see if he/she is established?
I think this may be the crux of the matter. Although the internet provides the widest exposure possible, the very process that enables that exposure also requires reducing the print to somthing that is far removed from its actual beauty. The result is that an exquisite silver gelatin print that should sell for several hundred dollars looks just like the $12.99 inkjet print.