What does it take to qualify as a reviewer?

You need to hang out at all the audio shows. You need to be a good schmoozer.
you need to remember EVERYBODY who is anybody in audio.
You have to kiss the right ass.
Then you have to be able to write a reasonable sentence.
And know what a paragraph is.
Beyond that, just be in the right place at the right time, and suddenly, you're a reviewer.
You need to want to write, and reviewing audio is just a thing you can do writing about!!!
OR
You can start your own website and write stuff.
Or your buddies who did start an audio review website can put your reviews in thier site.
OR
you can write reviews for all the sites like Audiogon, and Audio Asylum endlessly until you get noticed by one of the big review places..

Talent needed: can write a sentence, a paragraph. and have ears, and a place to do the reviews.
(If one lives in a box under a bridge, i do not think reviewing is for them.)

I agree with most of what Elizabeth mentions. But- It is apparent that, in many cases, ears were NOT a prerequisite.

Trying to be serious here, I'd say a GOOD reviewer would have, first of all, broad exposure to the great variety of manufacturers and designs that exist. That's a corollary of the problem with much advice given in online forums, you usually don't know how much or what background someone posting an opinion really has. Second, they'd have enough industry insider knowledge and technical expertise that they'd not recommend that readers go and buy some poorly designed product marketed by an under capitalized company bound to go belly up in the near future. Perhaps a bit of understanding about marketing and business would help in evaluation of products. After all, some very small operations have made great gear and been in business for many years and other upstarts with big budgets and grand ambitions have failed. Of course, writing skills would be a great help. Having an analytical mind that understand the basics of logic and that has developed reasoning skills balanced with the capacity for intense emotional involvement with music helps as well. As to "not having ears," I'd just chalk that up to the fact we are all different and respond to different aspects of music reproduction. Plus, it's impossible to use a piece of equipment in all possible contexts. Can a reviewer write an objective, dispassionate, and analytical review of a product that would accurately describe all performance parameters and equipment/room interactions?