If it's anything like Fine Art America, you'll be competing with many thousands of other people trying to sell their work.
The only reason I keep being on FAA is that my gallery pages on my own website are their pages.
Still have never sold anything thru them but mostly, my gallery is to show possible framing customers that I'm more than just a slap 4 pieces of wood together type of frame shop. I'm an artist as well.
All in all, the only one who is guaranteed to make money is the site people taking in yearly fees. Trust me, that is their primary goal in this.