Some time ago, the CEO of one of my clients had to leave the company during the M&A process. The CFO took over the responsibility for all the projects tasks which normally would have been handled by the CEO, like active participation in the talks and negotiations with interested parties, etc. The CFO was not a shareholder, so the chairman of the supervisory board promised a bonus if he would bring the transaction to a successful end. The CFO did a good job and the transaction closed to the satisfaction of all parties involved. But when the CFO asked for his bonus, the chairman told him that, unfortunately, the books were already closed on the deal and nothing could be done for him anymore.
I am not saying that this is typical behavior in todays business environment. No, we still see fairness, trustworthiness and reliability all around us. But there is a message in this story: Trust is good, but a little piece of paper with the chairman's signature is even better.