I'm TZ News's Reviews editor, so I guess I can make some kind of "official" statement.
If you're interested in being a reviewer, you can send me a PM inquiring about a position. I will ask for at least one sample review (depending upon how that one sample strikes me, I might ask for another). If the sample(s) suggest the writer is thoughtful, intelligent, and able to write coherently, I might give the writer a probationary position or ask him or her to join the staff outright.
But I also take the member's "temperament" into account. Staff members have to work together, and it is extremely unlikely that I'll offer a position to anyone whose public behavior is rude and offensive. (That doesn't mean that reviewers have to agree with each other; it only means that they be able to discuss their differences in a polite and professional manner.)
This kind of thing, I'll note, is a pretty good way of ensuring you will
not be asked to join.
Not all news staff are mods, but many are, because mods have already demonstrated their professionalism. Staff members are often mistaken for mods because their names are bolded, but all staff members (whether mods or not) get their names bolded.