If a randomly selected male and a randomly selected female have casual sex the direction in which this is most likely to be considered a favour is from the male to the female.

Maybe this is true, but the (overwhelmingly, I think) most likely situation is that it is not considered a favor at all, in either direction. In most cases, casual sex just isn't seen as a favor. I'm not a woman and I may be wrong about this, but I really doubt that many women are inclined to agree to casual sex out of a sense of obligation or altruism.

This makes the advice provided relevant.

The general advice of developing and following a strategy is of course applicable in all four cases, but that's just because the advice is so general. The reason I brought this whole thing up is because the particular strategy that one should follow will, I think, be importantly different in the casual sex case than in the other three examples. I think a decent strategy for a tall person, say, would be to accede to requests for help if the request doesn't require you to go significantly out of your way or put you at risk of significant harm. The same strategy would work for the strong person and the smart person. But it most emphatically would not be good advice for how a woman should deal with sexual propositions.

Many people (including me) feel that people with certain advantages do have an obligation to deploy that advantage for the benefit of others in certain cases. I think a tall guy who had a policy of refusing to ever help someone reach stuff unless there was something in it for him would be a dick. I do not think a woman who refused to sleep with someone else unless there was something in it for her is a dick. The "advantage" in this case, such as it is, is not obligation-generating in the same way. Seeing that example along with three others where some obligation does exist raised a red flag for me.

If I remember correctly, OrphanWilde is an objectivist, so perhaps his equivocation of the casual sex case with the other three has the opposite motivation -- he doesn't think any obligation exists in any of the examples. From that perspective, perhaps the fourth example doesn't stick out quite so much, but it is not a common perspective and it isn't mentioned in his comment, so I didn't really think of it until I read his reply and recalled who he was. In the absence of that information, I read his comment as indicating a somewhat unsavory attitude towards women's sexual autonomy. Now I see that my disagreement with him is probably in the opposite direction -- in how he thinks about the first three cases rather than the fourth -- but I still think the fourth example doesn't fit.