Does anyone have experience with what they call "app tender" sites like http://appcity.org/ http://appcity.org/ ? I've heard one anecdote about a guy who knows

Does anyone have experience with what they call "app tender" sites like http://appcity.org/ http://appcity.org/ ? I've heard one anecdote about a guy who knows a guy who bought a very simple iOS app for 10K, did some marketing on FB and made like 20K within a month. I'm more interested in any experience from the developer perspective selling apps on a marketplace like this. I've also heard the new iOS makes this easier to do.