not free lunch in the sense of 'free of effort'; but in the sense of somehow there is intrinsic inefficiency in the buy side or the sell side, which was OP's question.... so if you expand along that line of thinking, most of the ET threads are looking for free lunches, as if they can discover something 'sitting' there, something that others have not found yet.
what I am saying is that trading is not about finding something 'sitting there'.... it's about unfolding stories.... if I can only have 1 wish, that would be a fly on the wall when my pro boys decide their campaign to lift up the market and when they decide to knock it down... but alas such invitation I do not get, so the only way to figure that out is thru observing, with details I have laid out in my many posts.