If you're active on Flickr, you might want to check out their recently updated Best Practices for Organization guidelines.
http://www.flickr.com/bestpractices/Some of these points are good for sellers to keep in mind:
"Add meaningful titles and descriptions (but no price information or sales-y verbiage) to your content."
"Groups are a great way for members to share photos on a common theme. If you create a group, respect the rights of members by not making rules asking members to give up all rights to their content when adding them to the group. (Additionally, if you’re interested in setting up an official sponsored group contact our advertising team.)"
