Everyone is always up in arms about the non paying gigs.
A festival offers you to make a poster for a band or performer. You must send off 20 or so copies to the festival organizers. Your payment is 2 tickets to the festival which you won't use because it's on the other side of the country. Permission to sell the posters after the festival on your web site or flatstock is not automatically granted by the festival organizers or artist. You must create extra leg work to "approve" your poster and even then it's not guaranteed the performer will approve it.