If negotiations are successful, what are the penalties (if any) for double crossing them and attacking again when our position is more advantageous or their guard is down?

For example, a while ago we discussed the mechanic of coup de grace. I recall the determination being that it is an allowable mechanic but it carries a bit of "reputation" in the way that others view or treat you in the future. Does that sort of thing apply to double-crossing people as well?

After all, if they all end up dead, who's to say that we made an agreement in the first place?