Your description of your background in the body of your text would leave me to believe you are extremely experienced but your total time in your profile is only 1400 hrs. That is not really a large amount of time. This begs many more questions like are you a FO or Capt at your regional and how many hours total time does your friend have? If your friend is legally qualified and insured by a company to fly his own plane you are assuming an enourmous amount of authority when you start to assess (on the internet no less) his flying ability. For instance, ask yourself is my friend such a bad pilot I need to contact the FAA about him or not. If he isnt and you wont contact the FAA yourself, than make up some nice excuse to get out of his plane and dont bother feeling quilty about it. Hasnt someone else (like an examiner) already done that job?