I sell things from my own patterns. It cuts down on the number of different things I can sell (since I'm not a very experienced pattern person yet) but it seems to be the easiest way to sell my knitting.
I believe that you are usually not allowed to sell completed projects from a published pattern unless it states that, or you have made an arrangement with the pattern writer. A friend of mine is licensed to sell baby soakers that way from another person's pattern.
The other thing is that it is the written pattern which is copywritten I believe. So a baby hat on circular needles with the decreases in a star pattern doesn't belong to any one person, for example, it is the written pattern that belongs to that one person.