One could argue that even link sellers offer a "review" when determining whether or not to sell you a link on their site. Category sponsorship is a clear case of link selling, even if there are some minimal listing standards (relevance, written language, etc).
Matt Cutt's discusses this in a post at: http://www.mattcutts.com/blog/how-to-report-paid-links/, which if you haven't read yet (it's a few years old) and have the time to I would recommend. Here's a pretty solid extract otherwise: The purpose of the fee paid to a directory like BOTW would seem to be for the time & effort taken for someone to do a proper review & evaluate the site. On the other hand, if you're selling links & are doing just minimal checks to make sure the website you're link to is legal/not a bad neighborhood etc, the purpose of the payment would generally not be for the review, but rather the link.