Hi there,
The issue with affiliate sites is pretty simple really: does the site rely very substantially on affiliate content? Would it exist and still work as a useful site if you removed all the affiliate content? If the site exists only as a vehicle for affiliate links and you do as little as you can to meet Google's requirements beyond that, it's pretty much guaranteed to fail.
You can read much more about this in a very helpful blog post ("Googles Secret Guidelines On Thin Affiliates") someone wrote a few years ago. This is a key quote - and gives you some idea of where Google draws the line between "useful" and "thin affiliate" sites. In a useful affiliate site, the affiliate links and sales are a minor part of the site.