Assassination

With these points in mind I have succeded with every contract (civil or military) that I have accepted so far. In every case a victim didn't show up I could find a reason from the list above and succeeded in the next trial.
On the other hand there have been reported lots of problems with victims not showing up or refusing to land at the port of destination. Some of these problems seem to stay even if you use every trick in the book. In such a case your only chance is to reload a saved game from the time before you accepted the contract.