What are your moral principles?

But the lack of understanding is not a flaw, but a lack of training... Now, after this situation, he understands.

As paradoxical as it may seem, the more experience a person has in relationships, the less their opinion on the matter is worth, because they have repeatedly failed to determine whether a person is right for them or not, or have not been able to devote themselves to the person they chose. Of course, this refers exclusively to romantic relationships; if we talk about partnerships, the situation is reversed: the more experience, the more effectively you can act with each subsequent attempt, thanks to the acquired knowledge and skills. Given that 99% of couples represent the second type, one might ask: why bring up this topic at all? Because relationships in which partners offer each other something (attention, appearance, care, body, money, etc.) depending on their standards, are not genuine love (although they may develop into it later), and this test tries to present them as such.
In this story, Mary showed selfishness, as she put her desire to be with the object of her love above his own feelings for her. Her surprise at Robin's reaction clearly indicates that she has no remorse, which excludes positive selfishness - a sacrifice made for the well-being of the loved one, which he did not want, because his own freedom might be less important to him than not wanting to see her in the arms of another man, and this may be based not only on his own discomfort but also, unexpectedly, on care for her, assuming that he is confident in her love for herself, feels the same way about her, and expects that a night with someone else will be unpleasant for her. At the same time, after hearing what Robin said, Mary did not try to apologize to him and, moreover, on the same day, left with another person, to whom she had not felt romantic feelings before, which shows her as a person capable of changing the object of her love like gloves. As a result, it turns out that they both turned out to be unable to understand and forgive each other. That is, there are only three positive ways out of this situation: a) not to agree to the Sheriff's offer; b) for Mary: apologize to Robin; for Robin: accept Mary's apology, apologize for getting angry with her, and continue the relationship they had before; c) peacefully part ways.
About John, one can add the following - if there was some backstory about him having long-standing romantic feelings for her, and she felt the same way about him, then his actions could be explained, but since there is none, in this story he turns out to be a little loser, who just wants some kind of relationship, no matter with whom, or with the only criterion - beauty, as indicated at the beginning of the story, which makes his act even worse from the point of view of morality, which this test sings about.
In the end, it turns out that the only positive characteristic can be given to the Sheriff, because he kept his word (although he could have not done so without any consequences for himself), but this still does not make him better than the others.

Thank you for your attention... I absolutely do not regret that I spent more effort on writing my opinion than the author did on writing the test itself. Unfortunately, the last sentence is a lie.