I rather think this idea that men are manipluated through sex is overstated. To me it's a bit more of a game that's played with both parties getting what they want. Just because there isn't a statement of intent up front i.e. 'I'll give you 20 blowjobs for 1 tractor' doesn't mean that there is ignorance on one or other side.
I've just threatened Mr LaT with "if you don't let me win our Monoploy tornament then it's onanism for you for the next month"......(it's getting tense now, my lead has shrunk to 17/15.....first to 21 the winner)...... Fair enough, that is a statement of intent