How does the payment work? Does 100% of the money, minus listing and fees, go back to the shops who put the items in? Or are the items donated and the money is used on other things, like advertisement and things like that?
If the money just goes back to the shops who donated items, then if each item sent in is labeled with an approximate price that the seller would like to receive for it (discounted from how much they'd sell it in their own shop), then the person who is collecting the items and setting up the boxes would know based on that how to price the boxes, how many items to put in each box, and once the box sells, who to give the money to.
However if the money is pooled/split in a different way, like to give each donor a percentage of each sale, or to pay the person collecting all the items for setting up the listings, it could get a little more complicated.
I've gone over Pets Jubilee and I have no idea how they set theirs up. It looks like the items are donated, but I'm not sure where the money goes.