The Executive Coach should be selected based on their ability to identify an effect approach for coaching.  A Harvard Business Report recommends that if a coach is unable to identify the methodology they will use, then organizations should continue looking for a coach that can articulate their approach for coaching.  The methodology could be through 360 degree feedback or psychological assessment or other reputable methods.  However, they should be able to easily respond to this question.  Furthermore, it is important that the coach is trustworthy.  The coach and the manager or executive will likely share intimate aspects of their professional life, and possibly their personal life, and the coach should be able to be seen as one that will keep the appropriate confidences.  Equally important is the ability of the coach to demonstrate commitment to the employee being coached.  This commitment will help to garner commitment from the employee being coached.  Lastly, the coach needs to be someone that communicates effectively with the manager or executive being coached and should have a way to motivate others to perform their best while overcoming barriers to their success.