I'm guessing what you are actually saying is shutterstock won't accept your data and you are assuming the data acquired by the camera is not 4mp. Possibly, I'm not understanding your question but the camera doesn't select the number of pixels it us...
I too just recently purchased a refurbished SX50 so my response is not one based on complete familiarity with the camera. However, ...If there is a DOF preview setting on the SX50 I am completely unaware of its existence and cannot find any reference...
