Bad reviews drive sales if they're spelled well

Slate story here.  Interesting links to the relationship of the underlying research to the habit of some online sites of correcting grammar and spelling--could this be misleading given that it does affect purchases?  And then there's the question of whether there's hidden product placement in reviews for related products--the advertiser may be promoting its speakers in reviews for speaker mounts, whether positive or negative.  Presumably this falls afoul of the FTC guidelines, and competitors (and noncompetitors!) may also have something to say about it.