Re: Any art booth vendors that sell original paintings
I went to an art fair this summer, and a ton of people were selling prints (especially the ones on metal) as well as originals. Thinking of the people who were visiting, I didn't see anyone who I thought was looking around to buy someone's art and reproduce it. I think for most artists, our work is more valuable to us than it is to others.
The times when I have seen people steal artist's work it has generally been some company that produces consumer goods. Remember a while ago a woman accused a design company of stealing her art and using it on their stuff, like towels and cups and Xmas ornaments. I think she had had her stuff up on Etsy. It was quite the big deal. And then it turned out that she herself had stolen many of the designs they in turn stole. At any rate, what I noticed was that the designs were quite simple. Like a polar bear outline with a sort of quilt design imposed on it. Stuff like that would make good units of a larger design set. From what I have read, design companies like things in sets.
Also, I have heard that stealing designs on Etsy is huge, but we are talking like someone who paints glasses stealing someone else's idea for a painting on a glass or something. It is bad but it is not an issue that most of us will have to deal with.
Anyway, the only other people I have seen who steal art are online. And mostly they are using it to decorate their site. Which is annoying but small potatoes compared to a corporation that is reproducing your art on dishes.
I think you can put that you retain copyright in some addition or even just on the receipt or invoice you give with a sale.
As for someone copying your prints and selling them, I don't think so. It is not easy to sell prints, as we all know.
If your medium was photography, I would be more concerned because it does seem like that is stolen more often.