Amazon Product Advertising API - get review-rank

Question 1

Preamble: I'm not sure that I understand exactly what you are looking for here but I'll share my findings anyways.

I was able to retrieve the iframe URL for the reviews and was able to see the reviews iframe after embedding it into an .html page. I used the following attributes to retrieve the iframe URL:

Operation=ItemLookup&
ItemId=1451648537&
ResponseGroup=Reviews&
TruncateReviewsAt="256"&
IncludeReviewsSummary="False"&
Version=2011-08-01                 <= important: can't be less than this version
AssociateTag=<YourAssociateTag>    <= required when using this version, can be anything (not verified by Amazon)

The relevant part of the response:

<Item>
    <ASIN>1451648537</ASIN>
    <CustomerReviews>
        <IFrameURL>http://www.amazon.com/reviews/iframe?akid=<YourAmazonKey>&amp;alinkCode=xm2&amp;asin=1451648537&amp;atag=<YourAssociateTag>&amp;exp=2012-01-06T02%3A10%3A38Z&amp;summary=0&amp;truncate=256&amp;v=2&amp;sig=kjWPue1N75%2FiI1hW67XYApWxnKeT2tlT%2FJ1rw4WLlUo%3D</IFrameURL>
        <HasReviews>true</HasReviews>
    </CustomerReviews>
</Item>

Note that you will not be able to use this iframe URL due to the fact that (1) I've removed my Amazon Key and the Associate Tag that was used to create the signature and (2) it expires 24 hours after the call.

If you use the same attributes that I've used, paying close attention to the Version and AssociateTag fields, you will get a result with an iframe URL included.

I then embedded the url in an iframe:

<html>
    <body>
        <iframe src="http://www.amazon.com/reviews/iframe?akid=<YourAmazonKey>&amp;alinkCode=xm2&amp;asin=1451648537&amp;atag=<YourAssociateTag>&amp;exp=2012-01-06T02%3A10%3A38Z&amp;summary=0&amp;truncate=256&amp;v=2&amp;sig=kjWPue1N75%2FiI1hW67XYApWxnKeT2tlT%2FJ1rw4WLlUo%3D"/>
    </body>
</html>

Which looked like the following:

Amazon Review IFrame

As I said in the preamble, I'm unsure if this is what you are looking for since the requirements for the bounty was:

...to get access to amazons reviewrank informations

This isn't exactly the review rank information but the actual reviews and I take the meaning of review rank info to be more along the lines of the data itself (such as 100 reviews @ 4 stars etc.). However, in your question you stated that the iframe did not work:

However, testing with the params they suggest to get the Iframe, but it seems that now even the Iframe doesn't work anymore.

So I thought that I would at least provide you with the proper method of getting and using the iframe.

Question 2

Amazon has completely removed support for accessing rating/review information from their API. The docs mention a Response Element in the form of customer rating, but that doesn't work either.

Google shopping using Viewpoints for some reviews. I came across a good article for this

Question 3

I know you said you don't want to screen scrape, but as that is the only solution available, I have been using the screen scraping solution for some time and it has not caused me a problem yet, although I agree it is fragile. If my screen scraping code does not get what it expects, it will log an error for me to adjust the code, and it will degrade gracefully to just display a link to open the review information in an iFrame. This error has yet to trigger and the solution has worked great for us.