As a former manager of a portrait painter, I can agree that keeping the pricing simple for your client is important. You can even scare some prospects away by being too complicated in this area.
I think the bottom line is that there will be more profit from some portraits than others and I think this is probably just the nature of things when we're talking about a custom creation.
I experience this in doing web design. Some of my clients ask for more things on their site or they are simply more picky. Though I must admit that I've jokingly threatened to add a surcharge for any client that is a former graphic designer. Sites for them usually take at least twice as long to do! But, I've yet to do it cause I'm a softy.
To any of my former graphic design SOG clients reading this, I'm saying this with a smile.
