I agree with everything said above. I just want to add something.
Taking pictures as a favor for someone and getting someone to pay for something is completley different. There is a quote I always use from the Amercian Society for the Prevention to Crulity to Animals. It is something like this: "Don't give away baby animals (cats/dogs.) Charge for them. Even if it's a single dollar. You'll be surprised what people will take for free that they won't pay a buck for."
The same is true here. Once you enter into a business proposition, the standards are much higher. Here are some examples. People won't want the print to fade, so you'll have to get better prints made. They'll want it to be a standard size so it's easy to matte/frame. This will limit your crops not to what looks good, but to what fits a frame well. It will have to be to their standards of good, not yours. And people paying money for something will/should have high standards.
I'm not saying that you shouldn't try to do this. I'm saying that you can't expect to just jump in and do it. Do it for yourself for awhile. Show people the pictures and ask if they'd pay for them. Do your research before you jump. It just might be into deep water with sharks.