Can you please explain? In CS conferences there is generally a small pool of reviewers for a paper in a given sub-area (ex at a conference on systems some peop

Can you please explain? In CS conferences there is generally a small pool of reviewers for a paper in a given sub-area (ex at a conference on systems some people might focus on file systems). These reviewers tend to review each others’ papers since to be a reviewer you also must be an active contributor. I don’t see how any algorithm might detect this pattern of fraud without taking into account the merit of the papers.