Good cameras have all the controls you need, and make those controls fast and easy to operate. Better, great cameras let you program the camera do all the grunt work, like setting exposure and ISO and focus, exactly the way you would. Great cameras have a button dedicated to each important control.
What Sells Best On Shutterstock?
Some types of photos that sell best are Portrait Photography, Food Photography, Landscapes (usually with people) and fine art photography (artsy).