Nope these aren't exclusive...they sell on other sites...this is the first time I've ever put photo's on a pick your price site so I don't really know what is a good starting price...
On Cutcaster as well as on Zymmetrical, I let them set the price. You have to trust these agents have contacts in the industry and they know what the market can take. It's their expertise. Just let them do their job. I don't think it's wise that a contributor will start price competition, especially on the low levels you mention.
