Situations like this are not uncommon for freelance artists, writers, and musicians. The philosophy seems to be; "The skill comes FREE to you, so it should come free to me, too!" This same freeloader wouldn't think of not paying their dry-waller or mechanic, but artists are used and abused! It's all part of the education you need in order to survive. You soon learn to value your own work, and to defend your right to make a living by it!