who reviews questions on yahoo answers?

Everybody. Everybody is free to report questions and answers. What happens after a report depends upon the "trust" level of the reporter. It only needs one highly trusted reporter, or several less trusted reporters for a question to be removed.

Now, if your question is removed and you do nothing, then fine. If you appeal then your appeal goes to a staffer who makes a decision. If the staffer decides that your question was reported incorrectly, then whoever made the report has their trust level reduced and your question/answer is reinstated. A few weeks ago one of my answers was reported. I lodged an appeal and it was re-instated with a note that the trust level of the person(s) who reported it will be reduced.

Update: I see three replies to this question, including this reply, and they've all be down voted for no apparent reason. What a strange community this is *sigh*

The community of users do this, as Yahoo doesn't have enough staff for the task in question. They can only get involved when abusers launch an appeal.

Other users review the questions on Yahoo! Answers. That's all. Yahoo staff only gets involved in the case of appeals...they're not involved in reporting.