How can I? You won't accept any evidence other than a failed drugs test and he hasn't failed one. The facts that lead me to the conclusion are as follows:
1) There are world junior athletics championships held every year (there are two of them each held every second year, not sure the distinction between the two) and from the ages of 17-21 when he was eligible Mo Farah did not win a single medal of any kind in any year. Two events per year, 3 medals, 5 years, that's 30 medals and he didn't win one of them
2) This is hardly surprising because in the World championships and Olympics held when he was 21-26 he also didn't win a single medal of any kind at any distance
3) When he was 26 he began working with an American coach who has had 3 athletes testify under oath, at risk of perjury, that he had encouraged them and showed them how to dope
4) since that time he has won every gold medal at two Olympics and several world championships at 5K and 10K, something that no other distance runner has ever achieved.
That Pokster, is overwhelming circumstantial evidence, I'm afraid.
However let's be honest, we'll never agree on this. How's the kids and the golf game, in that order?