My understanding of sports betting is that value bets will win over the long term. Usually it is the bookmaker who is on the better side of value, so as long as there is trunover, they come out the big winners, not the punter. To turn the odds in your favour, you need to either be very good at assessing form and value, or pay for a subscription service which may cost thousands per year. It's a bit like share trading - 90% lose money in the long term, 10% make money, 5% make a killing. If you're happy with those stats, start small and have a crack.
