For me it would go like this:
1)Client & artist discuss concept, price & time frame
2) Half the total fee upfront
3) Artist sends the client a scan of prelim
4) Client suggests changes or oks prelim
5)A scan of the final piece is sent to client
6)If clients is happy, final payment is made. If not happy changes are made.
7)Client gets artwork, artist gets money
End of story
---PUNISHER KILLS THE MARVEL UNIVERSE---