When you say "some people", I am afraid you are over-estimating the number of gamblers/bettors who could be profitable in a consistent way to make betting their full time job, though. The majority of people is unable to reach such level of accuracy and end up losing money. Those who manage to get money from betting markets in a full time won't share their algorithms and strategies, so we would never see them offering tips or courses on how to become better at betting.
The majority of bettors are better off just keeping their regular job and using money they can afford to lose to bet, keep expectations low and allow wins to be a sweet surprise of the come our way.
The only way one could be one hundred percent sure to profit from betting markets, would be to establish one's own betting bookie and accumulate money from volume of bets.