Are there empirical studies showing that one sex is more sexually selective than the other? Initial research: I've found papers by Clark and Hatfield (1989) and Buss and Schmidt (1993) that seem to lend support to the idea of heterosexual females being more selective than heterosexual males. 

Motivation: I have constructed a game theoretic model of romantic advances. Within this model, it is possible to show that certain Nash equilibria are Pareto improvements upon others depending on which sex is more selective. Thus, I'm looking for empirical evidence as to which (if any) sex is more selective

Does anyone know of any other empirical studies that support or go against the idea that heterosexual women are more selective in who they date, have sex with or have relationships than heterosexual men?

References

Buss, D. M., &amp; Schmitt, D. P. (1993). Sexual strategies theory: an evolutionary perspective on human mating. Psychological Review, 100(2), 204.

Clark, R. D., &amp; Hatfield, E. (1989). Gender differences in receptivity to sexual offers. Journal of Psychology &amp; Human Sexuality, 2(1), 39-55.
As noted above, evolutionary theories suggest that (heterosexual) females should be more choosy than males, because they typically invest far more resources in raising offspring (men have enough time and sperm that their genes are going to be more successful if they adopt a scattergun approach!).

A disclaimer here is that, in humans, research on sex preferences is difficult because it is mostly based on self-reported preferences, and because these are likely coloured by cultural and historical norms. However, there is significant empirical evidence that females are more choosy. Searching on google scholar for "sex differences" and "mate preference" or similar will give you lots of options. Here are a few.

Here is a study which summarises, across many cultures, some sex differences in self-reported mating preferences. As predicted by Buss and others, the authors find that across all cultures men report that they desire more sexual partners than women. This is not a small effect. They also find that men are more likely to consent to sex after a brief period of time, and that men everywhere are more likely to be seeking short-term partners. 

Here is a more experimental paper where they changed the attractiveness and implied wealth of potential partners and found that men were more likely to go for short term, multi-partner strategies than women who were more likely to go for long term, committed relationships.

Of course, there are also many studies from other species, some of which show the conditions in which men become more choosy. This paper even includes a video of a female beetle trying to reject a male! 

This paper proposes a mathematical model which might also be helpful. Modern models are much more nuanced about how male and female choice interact.