Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
Your first mistake is not billing for art and print separate. They are not the same thing. The artistic process can drag on longer than the printing process in cases, so how can you or anyone else just not bill for it? It's one thing to type up some simple text or something....but once you start down the road of a actual design....IMO you better be billing for it.
S.O.P. for me has become asking folks to make a sketch and then snap and send a phone pic.
I've taken to "guiding" customers to Shutterstock to look over designs; I'll help them with search terms, and to search for vectors (but we can deal with whatever if they want to spend) and let them spend the time searching for it. I have some regulars that will just go there first now and send me what they want, I download it for what, $10, put the rest of the design together for $30 - $45 on a project like this, and done.