In the previous mishnah we dealt with the various payments owed by one who seduces a young woman or one who violates her. One of them is boshes, compensation for humiliation, and our mishnah teaches that its amount is not fixed. Rather, it is determined "lefi ha'mevayesh veha'misbayesh" - according to the nature of the offender who caused the humiliation, and according to the nature of the victim who was humiliated.
Two approaches to understanding "the one who humiliates":
According to one opinion: when the one causing the humiliation is an average person, the humiliation is more severe. For if he were an especially prominent figure - a king or a famous person - the victim would not feel nearly as humiliated; and likewise, if the offender is a contemptible person, there is not much humiliation in it, since that is simply the way of such people. It is precisely with an average offender that the humiliation is greater.
According to the opposing opinion: the lower the status of the one causing the humiliation, the greater the humiliation, and the amount is assessed accordingly.
The humiliation payment naturally depends as well on the standing of the one humiliated: if we are dealing with a person of prominence, the humiliation is great; but if we are dealing with a person of loose conduct, the humiliation is not so great.
Pegam (damage to value):
From here the mishnah moves on to discuss pegam, which is payment for the loss of a person's essential value. In the words of the mishnah: "ro'in osah ke'ilu hi shifchah nimkeres" - we assess her as though she were a maidservant about to be sold, "kamah haysah yafah" - how much she was worth beforehand, while a virgin, and how much she is worth now, once she is no longer a virgin. The difference in value between the two is the pegam. This is stated only as a method of assessment, since she herself cannot be sold; the reference is to a non-Jewish maidservant.
And why does such a difference in value exist? The Gemara explains that the difference is relevant in only one case: a person who wishes to buy this maidservant in order to marry her to his slave, and since the slave is dear to him, he prefers to marry him to a virgin rather than to a non-virgin. This difference in the slave market is the pegam, and the same law applies to any person who suffers this sort of damage: the assessment is made according to what they would fetch in the slave market, and the difference between the two figures is the payment.
It is worth noting that there is an extensive discussion as to why the assessment was set on this basis, given that it is a purely theoretical estimate, for a person cannot sell himself as a slave. Some seek to base it on a person who sells himself as a Hebrew servant, but even that is not a precise criterion, since a Hebrew servant is never sold permanently under any circumstances. We will leave this matter for another discussion.
Kenas (the fine):
In contrast to these two payments, the fine established by the Torah - fifty shekel - is "shaveh be'chol adam" - a uniform sum for every single person. In the words of the mishnah: "ve'chol she'yesh lo kitzvah min haTorah - shaveh be'chol adam" - any payment for which the Torah fixed a specific sum is universal and applies to all, whether the person is prominent or of low standing, and his background makes no difference whatsoever. Once the Torah set a fixed sum, it is the same for everyone.
In summary: in this mishnah we learned that humiliation is assessed according to the one who humiliates and the one who is humiliated, and the commentators disagree as to whether it is specifically an average offender who increases the humiliation, or whether the lower the offender's standing the greater the humiliation; pegam is assessed by the difference in the value of a maidservant being sold before and after; while the fine, like any payment for which the Torah fixed a set sum, is the same for every person.