Hilchos Rechilus, chapter 6, section 8 9

It is forbidden to accept rechilus even if the speaker told it innocently and did not mean to start a fight.

If he sees clear signs (devarim hanikarim) that the person really did speak badly about him, he may believe it — but only when all 5 conditions are met:

1. There is no way at all to judge favorably.

2. The signs are really clear, not just a little clear.

3. He saw the clear signs himself.

4. Knowing about the story will help him in the future.

5. He may only believe it for himself. He may not tell others, and certainly may not cause the person a money loss or hit him.