It seems fairly clear to me that merit is awarded to good posts 99.99% of the time.
Your numbers are quite optimistic 
From the many merit abuse threads I've seen, and considering 281640 sMerits have been sent until last Friday, I estimate a 2 digit percentage of this to be Merit abuse. But those came from the 600k sMerit airdrop. If you find a Merit source making very bad choices, he may be removed as a source once reported.