How do you go about pricing art work?

I'm not sure if this is in your field of expertise but since you run buisnesses I thought you'd be able to help.

I'm planning on starting a website where I sell peoples art work for them and then take a cut from the sale, the idea of this buisness move is that they get their art work on an established site (well it will be if I get it off the ground), which means affordable publicity because its only paid for when a painting is sold and it means they dont have to spend the money on their own website.

I have two problems though, first how do I get the paintings, people arent going to want to send their work to a stranger who could potentially steal their work, but how do I make it reliable for a custommer and garentie they get the art work they ordered on time?

My other problem is also a difficult one, how do I price an orriginal piece of art work? most of the artists I'd be working with would be starting out and using it as a away to make it big so to speak, so I could sell their art work at a low price, but obviously this isnt in either of our interests if were to make a profit. I dont know how to decide on how much a piece should cost, I cant sell them like a mass produced product because they are one offs, their not famous yet so I cant make it too expensive, but the idea is to help them become famous so we can sell the work at a relativly expensive price but then comes the difficulty of is it affordable for the consumer?

Any advice you can give me would be highly appreciated.