We don't. We differentiate between search engines that are _all_ affiliate laden links and sites which have a degree of advertising. If an editor can not tell what is advertising and what is 'real content' (be it proper search engine results or just a review), then the site will get rejected.
Unique content is the name of the game, but if we can't see the content due to heavy advertisments or affiliate links - then it's doubtful it'll get listed. Especially if a webmaster tries to hide the affiliate links using 'onmouseover' events and the like - it just makes an editor even more suspicious that a site has something to hide: and, hence, make them even more reluctant to list it.
If, for example, a shopping directory site had a large number of affiliate links - then it would not be listed, but if it had reviews of the majority of the sites, then it _may_ be listed. No site is guaranteeded a listing, but if you can "show the editor" that it has content which is useful to the third parties, then it probably will be listed.
[edit: corrected spelling of suspecious to suspicious]