Hi there
I've sold a few on fotolia. I put three or four pics up just to check it out and occassionally I get an email to say that I've sold a pic. It's these two here :
Photo: inside a hot air balloon © Jennifer Farley #686385 ,
Photo: balloon and fields © Jennifer Farley #686383 ,in case anyone needs a picture of a hotair balloon.
In terms of money, it's crap, unless you sell a LOT. Even at that, these kinds of sites really do take advantage of photographers. Your friend might do better selling photography through his own website, maybe?
all the best
Jennifer