Also limit review to be written X time after the product arrives. So many useless reviews that just said they received it and they are going to try it later...

Those reviews always amaze me.

And the people who answer one of the questions with "I don't know", too. Why did they bother typing anything at all?

My theory is that some people can't imagine that people aren't talking specifically to them. You see them in chat rooms answering every question as if it was posed them to directly, even when it was obviously directed at someone else.

In the case of amazon questions, this is a lot to do with how amazon handles them. If a new question is asked, amazon will sometimes send emails to people who have bought the product with the question. It's quite easy to see how someone could think this is directly addressed at them.

Why do you feel the process would be too expensive for most products? That is, let's say the review process might cost the merchant $5,000 on a one-time or biannual basis or whatever--does that seem like an unreasonable charge to take reasonable care that the products offered on the marketplace are authentic, of good quality, etc.?

I'll bite: Honest reviewer says that product works fine...for the first week or month. Wait for a year before allowing them to sell? Not doable especially on millions of new products.

Maybe reviews should be limited only to certified buyers or only those should be added to stars /rank.

Who is waiting a year? Just sell right away. The professional reviewer only has a few hours per product anyhow. That's enough the tell if the product is fake or deceptive. (Or if obviously fake, the quality of the fake :))

If you want to test longevity Amazon could track warranty repair / replacement claims.