I am thinking about buying a used camera off a mulitude of posters. What I am curious about is camera hours. How many hours is a camera "good" for? or what is too high a number to buy used? Also how much money should be taken off for use? Whats a good resale value of a camera w/ 50hrs? 100? 200+? I am a new user and just curious about lifespans and resale values.