Here is a result of 10 minutes research: (nicks and words are same at a lot of products)

"Great model" comment along with 3 stars rating look absurdly. I see similar ratings at other vendors (fortunately not mine) very often, when a customer is saying that is good or great job, and give 3 stars. Probably it happened when a customer write his review and press rate button, but forget to choose appropriate number of stars, and it give default 3 stars. If it were 5 stars by default we had more 5* products, I'm sure ;)

Maybe if a customer rates a model they purchase and they do a 1 star or 5 star review, might they get a screen that encourages a text response... Like this:

Thank you for your honest rating of this product.  We encourage you to post a comment to tell everyone why this product was not to your liking.

Thank you for your high rating of this product.  We encourage you to post a comment to tell everyone what you found so great about it.

I'm wondering if the default 3 stars is more of a bane than boon... people don't seem to know that if it's a 'great model' then it should be more than 3 stars, but they seem more concerned about doing the comment, not thinking about the stars.  Might be better to have no stars as default.

@Andy: These are very good ideas. And yes, it might be better to have no stars as default.

@Alex: :)