I don't know what I would do, but I guess it depends on the quilt- is it obvious that it's someone's pattern- I mean is it applique or something intricate? Or is it a simple geometric design or "vintage" blocks that have been around for ages and someone happened to publish a pattern using them? If it's the latter I wouldn't assume that they used a pattern, but may have come up with it themselves. If it's the former, I don't know what I would do. Maybe ask them about it, about the designer, etc. There may be special circumstances, maybe they got permission if they are raising money for a charity, etc. If they seem shifty about it, I would maybe try to get the name of the shop and a surreptitious photo or something to pass along to the designer and let them know about it so they can decide what to do.