Furthermore at least one person I know (er, myself) picks up on any sort of test-like or game-like or we're-judging-you-so-you-better-not-screw-up-like context and starts acting in extremely confusing/uninformative/atypical/misleading ways so as not to be seen as the kind of person who is easily manipulable (there are probably other motivations involved too). Any incentive structure I'm put under thus has to somehow take this into account, even e.g. the LessWrong karma system. Explicitly manipulative socially mediated praise/M&Ms would strike my brain as outright evil and would stand some chance of being inverted entirely. That said I don't get the impression this sort of defense mechanism is very common.