From Grace Note's comment in this answer, I was surprised to find out that the auditing system that is supposed to hinder robo-approvals is not active on math.stackexchange.
I remember seeing this a long time ago, after which I thought these were already in use.
(If this has already been discussed, my google searching skills must need some work...)
For those of you who might be unfamiliar with the scheme, here's a brief description. A review audit is a task in a review queue, just like any other item. However, if the user takes the wrong action (passing a bad post or punishing a good post, for example), they are penalized, and repeated failure causes their privilege to review to be temporarily suspended. The stats on audits can also be reviewed by moderators in order to investigate repeat offenders. It is designed both to catch poor style reviewers such as robo-reviewers, as well as to educate and realign folks who do genuinely want to help but are off-kilter to the standards of the community.