Regarding doping it turns out EVERY medallist was tested in a strict London 2012 operation so those who leave with their medals have left with them fairly.
That's a very naive statement.
Athletes either dope months before the event so they can put up a superhuman training regimen or they use blood doping, which is undetectable in a urine sample.
In order to truly catch cheating athletes, sports need way more out of competition controls and the introduction of a bio passport. Until then, only the truly stupid athletes get caught.
But even then, cheaters always have a few years head start to the testers. We know what lengths athletes and sports federations will go through in order to win. Would anyone dare to guess how widespread gene doping might be in sports?