Interviewers write up questions asked, candidate solutions, and their commentary and hiring recommendation. Those writeups are sent to a hiring committee which reviews all the candidate's feedback and makes a hire/no hire recommendation.

If the committee sees a brainteasers, disagrees with a question, spots inconsistencies in the feedback, etc., they moderate their use of the feedback or ignore it altogether. There's also a mechanism to send feedback to the interviewer, which they can use to let them know a question is appropriate, banned due to having leaked, etc.