I had a friend who was a flight instructor out of Pontiac MI. He mentioned to me the examiners there would fail people on Commercial checkrides for the slightest little flaw in chandelles, lazy eights, or eights on pylons. I assume they would use the Detroit examiners.

I've signed off five people so far for CFI checkrides. All passed. One was with a DE and the others were with the Feds themselves. I know of one DE in my area who does a one hour CFI oral and about a one hour flight for the checkride. Another has orals that last six to eight hours(including a break or two). So there's even variability in the same region. As far as reasons why people fail, the six to eight hour oral DE failed a guy three times. First he didn't have an 8710 form , second because he didn't have a clue how to teach(that was the pink slip), and third because he descended 3000 feet down to 500AGL during a simulated engine failure, looking for the checklist he lost, and doing absolutely nothing else. The guy didn't know what he was doing, how is he supposed to teach someone else? Not all of the failures in whatever statistics you see are due to FAA cruelty against people on checkrides. Some people just shouldn't be there.

My students have said that some of the best experience they got prior to the checkride was when I gave them my one of my problem students to practice an hour or two of extra ground instruction with. None of it was logged or paid for. I'll eavesdrop while I do paperwork nearby, to correct the "instructor" if necessary, and also so I can debrief with him/her later. The student gets a little extra free ground training(under my supervision), and the student CFI gets practice teaching a real student (instead of me playing dumb). I don't charge either of them for it. Another CFI told me one of the best experiences he got was taking his grandmother up for a flight and teaching her how to fly and even land the plane. Teach your friends and relatives for fun and practice. Explain to them why you need them to help, and that you want honest feedback on your teaching techniques to help ensure your success later on. Become an instructor before you even take the checkride.

Rather than thinking about this in terms of whether or not you'll fail, think of it in terms of whether or not you'll be any good at the job you're applying for. The goal is to be a good instructor, not just to pass a checkride. Focus on the bigger picture, and you're more likely to pass. What are your plans after you pass the checkride? Do you even really want to teach, or are you just doing it because you don't have any other options? An FAA examiner told me that he makes checkrides harder on people who act like they don't take pride in what they're doing, or care about the quality of their instruction. They can smell it on these people. The FAA's goal is to populate the aviation world with quality instructors who will teach new pilots good airmanship, good procedures, and safety. Not everyone is cut out for it. Of course if the examiners are just out to meet their quota of failures, then none of what I wrote may matter, but if they can at least see that you care about what you're doing, they might give you a chance.