Where did you get this from?
Google has demoted rival comparison shopping services in its search results: rival comparison shopping services appear in Google's search results on the basis of Google's generic search algorithms. Google has included a number of criteria in these algorithms, as a result of which rival comparison shopping services are demoted. Evidence shows that even the most highly ranked rival service appears on average only on page four of Google's search results, and others appear even further down. Google's own comparison shopping service is not subject to Google's generic search algorithms, including such demotions."
> Google has included a number of criteria in these algorithms, as a result of which rival comparison shopping services are demoted.
Sounds like a jump to conclude they were doctoring results from "they modify their ranking algorithms".
" Evidence shows that even the most highly ranked rival service appears on average only on page four of Google's search results, and others appear even further down. Google's own comparison shopping service is not subject to Google's generic search algorithms, including such demotions."
They were really not.
For every search you assume you will be given the more popular matches, what they were doing was purposefully bypassing their own algorithm to their advantage, giving doctored results.
There wouldn't have been any problem if they promoted their service making it clear it was not part of the search results.
EDIT: For a counterexample, google "flights price compare".
You will be shown a small form at the top from which you can use their own service.
It is clearly separated from the search results, which show the actual most popular websites for flight comparison.