• I dislike the suggestion that natural selection finetuned (or filtered) our decision theory to the optimal degree of irrationality which was needed to do well in lost-in-desert situations involving omniscient beings...
• Therefore, my analysis of hitchhiker scenarios would involve 3 steps. (1) The hitchhiker rationally promises to pay. (2) the (non-omniscient) driver looks at the body language and estimates a low probability that the promise is a lie, therefore it is rational for the driver to take the hitchhiker into town. (3). The hitchhiker rationally pays because the disutility of paying is outweighed by the disutility of breaking a promise.

I recommend reading the off-site lead-in post Ungrateful Hitchhikers to see why the above points don't address some of the implications of the argument Silas is making.