You can not copy and resell a pattern (without permission). Once you have made an item, it is yours to sell. The grey area is if someone says you can not sell something made from their pattern. First, I don't think they can do that (after asking an IP attorney). Second, if it bothers you, give the pattern owner credit (at a craft fair, have a small card printed with the pattern maker's info). Third, at your local craft fair, have you EVER seen someone walking around policing the patterns? I really, really don't think this is a concern. Now, if you are making and selling many, many items, the questions may come up. But, if you are concerned about this, then change the pattern to make it different, adding your own spin on the idea.