I don't think it would be possible to dramatically increase the size of a penis. Creams and pills may allow for a much harder erection thus giving the appearance of a larger penis, but to actually make one bigger or thicker I think would be more trouble than it's worth.
Dealing with adult every day I can say that yes.....some guys and shemales are naturally that big. It's kind of like a woman's breast. Some are bigger ands some are smaller. The bitch is they can do something about both situations is they choose. I don't think I'd want somebody knifing around my cock for a spare 1/2 inch or so