I understand being uncomfortable with this kind of justice, but I think it is admirable in most ways. It was quick, which I think has a positive impact on the offenders. It was evidently not unfair, or at least you do not assert that your friend was not guilty. And, it showed an element of mercy. You seem offended that they accepted the amount that the group could muster in lieu of the amount set by the court. Would it have been better if the judge had said that your friend should be put in jail until the full amount was paid? A quick court held in a gas station that renders a just verdict and shows some leniency in the penalty, is every bit as appropriate as a court that meets two months later, in a giant marble clad edifice, with distinguished well paid attorneys and honorable, black robe clad judges.
I'm offended because this was the type of activity I might have expected in some 3rd world country. I guess I'm used to a justice system which doesn't require one to pay cash to police officers.
The reason I put "Court" in quotation marks was there was no judge involved. The word kangaroo comes to mind.