Our guild just had the first of seveal quilt show board meeting Monday nite. This very question came up, so here is what was said--short version.
They have to be clean and odor-free. If there are any odors--smoke smell from cigarettes was the main one, it can be removed from Odor Eaters. That and hanging out on a nice sunny day--backing side up.
We made the rule that there will be signs up advising entries that they have to be clean, and odor-free.
You can't imagine some of the messes we got at the show a few years ago; cat hair all over it, a dirty-house smell, ect, ect.
We are having to turn ourselves into the 'cops' for quilts being "pristine."
Mariah