Getting your value inplay

[1878]

I was speaking to a guy recently who claims his sole means of income comes from his betting. Now most of us know that the bottom line of making a profit is getting value about your selections, now his method for this was that if he can't get it pre race he will leave it unmatched and inplay on betfair at whatever he perceives to be value for his selection. Now my argument to him was surley this method can't turn profits over the long run because you are guarenteed to be matched on every single loser and then only a small percentage of the winners I'd say. Now his argument back to that was, if you were willing to back it at blah blah price before the race then nothing has changed But obviously is has, the horse has either dropped back or looks to be struggling for the price to drift inplay and you end up matched, is this a valid way to get the value you need to turn a profit? what do you all think??