Bad Each Way trading?

[OvergrownHeffo]

I read somewhere (I cant seem to find it now) that in regards to bad each way bets, the place market on Betfair tends to come in before the race kicks off - I cant seem to find any data to backtest this, anyone know if this is true?
I've been trying to "sell the shovels in a gold rush" so to speak. When I see a big promotion on a bookies website for a specific horse or whatnot, I'll try get in early on betfair before the lay bets come in and its been working well so far