I just want to state right off the bat that I am by no means an expert in selling stock photography. I sell on two sites, Dreamtime and Can Stock Photo. At one time I sold on FotoFactory too. All three of these companies have no yearly service fee, and gave me some exposure with out laying out a dime.
When you choose questions you should ask:
* How long has the company has been around?
* Who will own the rights to your photo?
* What fees if any will you likely generate from each photo?
*How are you going to be paid for work sold? When can you be paid for your work?
* What percentage will you make on your work?
The reason nothing ever sold on Fotopfactory.
Out there in the Stock Photography world Getty reigns surpreme. Their pay out is 80/20 in Getty's favor, so if you are interested check out: