Google supplemental results

I just noticed that I have lots of my pages of my zlio shops (more than 50% of all site pages) placed by google in its supplemental results index. Well, this is not a good thing. Here is a summary of what I found in Internet on the topic:
- google returns results from its supplemental index only if it can't find a page from its normal page that matches the query
- google doesn't completely ignore supplemental pages
- your supplemental pages will not be returned as a result of a query to generic search words, they will be listed only with search words such as 'red baseball cap with a little black on it with a gray NY logo'. Not very useful, isn't it?
- supplemental pages are far more rarely indexed by googlebot than the normal ones. I saw a supplemental page indexed by G a month and a half ago. In the same site the normal pages were indexed 3 days ago.
- you can check if you have supplemental pages by typing in google: "site:mysite.com". If a page is from the supplemental index this is marked in the results.
- G punishes pages for duplicate content by moving them to sup

Now we see that this is not good and we need to avoid it in order to gain more traffic. The question here is how? Here is my findings:
- most SEO experts advise that the best way to escape from the so called supplemental results hell is get more quality backward links. They advise that just creating a website for the only purpose to link to another is of no use and webmasters should strive for quality backward links and the quantity is not important.
- my findings on the above show that this is not exactly correct. I saw zlio shops with backward links from their owners' blogs. Even if the site doesn't have other backward links besides this one, it still has all its pages in the normal G cache. Of course if you are linked from sites of higher quality, the better, but it still seems to me that every backward link works for this.
- try to avoid duplicate content. This is extremely difficult for affiliate programs like Zlio because every page that sells an item I sell looks almost exactly the same as mine. Try to put more quality and related text on every place on your pages you have access to.
- Do not use the copy/paste method. Especially avoid doing this from high ranked sites such as wikipedia, etc. Instead of copying the text try to modify it so your content be unique.