[cabalamat]

> what action comes as a result of a review?

Dissemination of information, which can lead to people making different decisions. For example, a would-be purchaser may feel a price is a bit steep but would have bought the book anyway, but after reading the reviews decides not to in solidarity with the other reviewers.

Or an author might get feedback that their fans aren't happy with the pricisng structure, and may take their publisher to task because of it.

A market is essentially a distributed information processing mechanism. Seen in this light, information transfers that are not buying/selling can be seen as part of the market. For example, haggling has always been part of market behaviour.