zoeexx: That's always a worry, but it's usually not as bad as your own fear of it.
The easiest thing to do is see how well people online take to your art. If you find that you get great responses from people on dA, on Gaia, CA, or any other art site, then you don't have much to worry about.
If you are just starting out in art and your art isn't very good yet, then it might be best to hold off on doing Alleys and use the time you'd spend preparing to practice arting xP
This isn't the thread to post your art, but you could post some stuff in the Pricing, Assistance and Suggestions forum (it's under Minishops) and ask about both Gaia gold prices and RL print prices. You could also ask whether people think this could sell, which might net you more replies since it won't force people to think about concrete prices (but it'll also yield many false positives).
A more difficult and risky thing to do is rather your stuff and get a table! There is no better way to see if your art sells than to try to sell it! It might be best to share a table with someone who has at least a couple of Alleys under their belt, since it'll be cheaper for you and you'll have their art drawing additional people to your stuff.