Rumour has it that Google quality assessors are instructed to detect which websites belong to 'true merchants', by checking for such things as shopping carts, return policies, etc. True merchants are deemed to be good, affiliates are bad. What is not addressed though is the fact that many 'true merchants' are also affiliates themselves.
A merchant (what we sometimes refer to as a 'Brand') may sell widgets, but not red widgets, oval widgets, or talking widgets. It can still sell these products as an affiliate however, using just a couple of hundred words of lightweight text, buried amongst reams of ads for it's own products, and survive a manual review, whereas a 'true affiliate' with many pages of clear, focussed information which is really useful to a searcher is labelled 'webspam' and penalised.
The result? A poorer quality experience for visitors, and greater difficulty for those searching for information; something there is a rising clamour about amongst webmasters.
The objective of the manual assesment programme is laudable, it is in all of our interests that people continue to use the Internet more and more for finding and purchasing products but the current guidelines have had the unfortunate side effect of encouraging merchants/brands to venture, as affiliates, into all sorts of vaguely related products that they do not have any real expertise in but which they can, nevertheless, dominate, to the disadvantage of visitors. Time for the guidelines to be looked at again, perhaps?