I think there are a lot of factors that weigh into whether a player is covering up or is honestly surprised at test results. I have little faith in the accuracy and broad sweep of these drug tests, and assume that 25% are false. There is close to a 10-20% inaccuracy with almost all medical tests, esp. of this nature. Add in the countless legal supplements aimed at all athletes which have untested substances and thus have a good chance of setting off a positive result. (and yes, even meat loaded with growth hormones)
So how do we know. There are physical signs, performance signs, player history... etc, with steroids, the facial changes are key. But this approach is hardly foolproof.
In any case, I hope Michael C can continue to get in a lot of work on the side, whatever that is, because the penalty is extreme for a first time offender. It sounds like something that murderous Philippines president would deal out.