I've worked at Amazon, both in the warehouse management division as well as AWS, and the whole "bar raiser" phenomenon is mostly just marketing fluff. There are a handful of engineers who don't mind interviewing (or at least hate it less than most), and they get picked often to be part of the interview circuit. After some number of interviews, you are considered one of the mystical "bar raisers". However, in my exper…
Bar Raisers do go through a round of training every year or so. Regular interviewers themselves are encouraged to attend a program called 'Making Great Hiring Decisions' every once a year or so. AFA engg roles are concerned... because the interview process is distributed, and because Amazon is growing too big too fast, there is a high chance that a lot of 'B' candidates get hired, but the general consensus is that th…
This is probably completely wrong , unless all of your B candidates are being hired at very low levels only, and none of them ever get to participate in the promotion process.
Additionally, most tech companies are really bad at dealing with low performers in general (they tend to stay around too long).
In any case, my sources are completely empirical, having managed large numbers of people at a number of tech companies (and thus watching things like what happens to B candidates during cross-organization score calibrations, etc), as well as mentoring and helping managers with some of these issues.
I'd love to be wrong, but I have yet to see a company where the hiring of B candidates did not have significantly more impact that was expected.