There a few show stoppers that will end a check ride pretty quickly. The FAA doesn't give the Examiner any choice in the matter and if you think about it, even just a little, the check ride should end with the Notice of Disapproval.
DPEs can NOT allow an applicant to exceed any aircraft limitations or break any regulation. That means the Examiner will likely stop the applicant before the issue happens. When that happens it's called "examiner intervention" which means the ride is over and results in a Notice of Disapproval. I've heard many stories from pilot examiners. One Examiner had to stop an applicant from climbing in to Chicago's Class B airspace and just recently another Examiner had an applicant attempt to fly an aircraft over gross weight.
Anytime an examiner has to take the controls to recover from a bad situation is also means for the Notice of Disapproval. You know those situations where your instructor quickly grabbed the controls to save the day? Well you don't want any of those situations on a check ride. I've seen these situations a few times. They are usually the result of one of two issues. The first issue is the applicant just wasn't trained sufficiently or correctly. For example, I've been spun several times on check rides. The second issue is the pilot exceed a personal limitation. For example, the applicant choose to fly on a day where the winds are 20 gusting to 30 and the only runway available results in a cross wind of 17 knots. I'll ask during the oral what is YOUR max cross wind componate. During the debrief I will ask why you went flying when you said you wouldnt fly with more than an 8 or 9 knot but the current cross wind was twice that! (I actually had an applicant tell his reason was he knew I would save the situation if it went bad. Unfortuatly for him, it did).