Dave Landers touched on the point I wanted to post - Whatever it is, from artwork to utility pieces, they are worth what someone else will pay for it.
The ideal case is where both the buyer and the seller end the transaction feeling like they made an excellent bargain!
I'll often have pieces I don't think much of and did not take much time to make sell for more money than a well thought out design that took a ton of work to make... As well, over the years (3 years now) that I've regularly been vendoring at various local markets I have found that the audience is variable as well as the price they'll pay.
One week, I might sell a bunch of bowls and turned stuff, the next week I sell nothing, but I manage to sell things like the crates I make (they are not even nicely finished or pretty) to carry my wood items into the market, or other flatwork.
As well, One week I might see several people admiring my work and saying "your prices are too low!" (though they don't really buy anything) and the next week, the crowd that comes by thinks I am overpriced! (without even changing my price tags between markets)