The rating scale is pretty simple, and has been discussed in other threads. If you own a card, you can click on it in your collection and assign a rating from 0 to 10. Your "vote" goes back to Totem, and they tally up all of the ratings. The average of all the ratings from all of the customers who have rated her card is shown as its average rating. When a card is brand new, the average rating can jump around a bit until there are so many votes cast that no new vote will move the average perceptibly, although it's theoretically possible for any card's rating to change over time.

Even though the average ratings are displayed to two decimal places (the nearest hundredth of a point), each individual customer can only assign ratings in whole numbers. If you think a card is worth way more than a 9 (which would put it in the middle to even below average of all cards), but not quite a perfect 10, you have no choice but to assign your own rating either too high (a 10) or too low (a 9).