(Thanks for asking Byzantine, I was rushing and too generic.)

If something like that happened to the responder and they dealt with it positively, then it's obvious: share that first hand experience. Lacking that, maybe there is a 2nd, or 3rd hand story that could be brought in. Not to tell the distressed person this is what YOU should do, but to present an alternative so they can decide if this may perhaps work for them too. If there is no real story, sometime just possibilities of alternative interpretation or alternative reaction could be offered. There is always more than one way of looking at things, and more than one way of dealing.

For example. Let's say someone writes that a friend did something awful and goes on how terrible it was, and the friend shouldn't have and how now this friend tries to say she is sorry, but the person does not believe the friend cares about them at all, and only tries to make herself feel better.

A reinforcing response would be to totally agree with a speaker: "You don't need friends like this". "Don't be pressured into forgiving her"

A positive alternative could question assumptions about why the friend did it, could point out that if the friend really did not care about this person, the friend would not feel bad about screwing them and would not care about seeking forgiveness. Yes, of course, the friend will feel better if she is forgiven, but that does not mean that's the sum total of her motivations.

The point of a positive response would not be to necessarily change the mind of the person about the issue, in this case whether or not to give a friend a second change, but to disarm the emotional charge that makes them not see things quite clearly.