keyword domains with content that is duplicate from their merchants do just fine.
There seems to be a significant way in which Google looks at comparison pricing engine websites.
It is almost as though they snapshot the quality of content against the "big guys"
Since most of the big players simply mashup their content by blending in POI's, reviews and various other elements, it might be a case of not having alot of high quality text to "score" and therefore demote against.
Let's face it, most of the those websites simply collate already existing results.
Interesting note how unique content websites have tanked. Seems like an about-face considering the mashups and duplication we see currently