Trading the Betfair markets is most definitely a genuine earning opportunity and for those who are determined and committed enough, it certainly can and does replace a full time job. And then some.
Yes you can make money laying horses on Betfair but it is not as easy as you think many punters wander into this with the understanding you have typically N-1 runners in horse race on your side where N is the number of horses in the race and 1 is the horse you have layed to lose the race.