i agree with lucky ... If he's betting 20 bets a night, then he needs to hit at least 12/20 every night to make that kind of scratch (more like 14 but i'll be conservative). Is that impossible? No. But it's incredibly difficult and very very unlikely. The more bets you make the more risk you take on, thus greatly increasing the likelihood that you're going to lose. If he has some kind of spreadsheet that is documenting the bets/wins/losses etc. and you can verify it's not being doctored after the fact then i'd say pick and choose one strong play that you agree with. Again if he's truly hitting 60-70% then chances are your one pick will be a winner. Personally i think he's pulling your leg.
the only other explanation is that the bookie he's using doesn't know what he's doing and giving bad lines or incorrect juice. I've heard of private bookines screwing themselves over like that. If it's on online book then no way