The content of the positive reviews is usually noise, but the percentage of negatives is generally meaningful, as are the contents of some of the negative ones.

On Amazon, you can still get some value from the 1-3 star review contents, but the average star count (which is similar to eBay's % positive ratings) is almost meaningless since any number of negatives can be outweighed by near infinite fake 5-stars. That doesn't seem to happen as much on eBay (although I'm sure it does still happen).