That's what brain is for
Does someone with K/D score 10/3 have a reason to plug? Chances are low, so here applies presumption of innocence.
What about player that has score 3/10 and disconnects right after he's killed? Pretty obvious, most of the time.
Rather simple system, in my opinion. I don't see how you can have trouble understanding it.
Hurr, darr. This feels like talking to an extremely ignorant wall, but here we go again:
1. The rules don't mention that banning d/c's is not allowed.
2. probability =/= certainty. Getting a bluescreen after giving firstblood is worth a ban, but plugging with 9-0 'cos you forgot about an important appointment should not be punished? Bullshit.