I quite often see watercolor paintings which have been poorly framed primarily because the picture being framed was not totally flat due to the cockling or wrinkling that usually happens to watercolor paintings after they dry.
I have just posted an article on my www.paintingwithwatercolors.com website about how to remove the wrinkles or cockles from the paper of your watercolor painting after it has dried. There is also  a short video of the technique at the end of my article. Here is the link: http://www.paintingwithwatercolors.com/picture-framingremoving-cockles-from-a-watercolor-painting/
Happy painting,
Joe