sentences:  Accordingly, competitors such as Epinions have devised strategies to filter out poorly written reviews as well as prevent users from gaming the system, by using algorithms to prevent groups of users in "mutual admiration societies" from giving glowing reviews to each other's products.A continuing problem for all businesses in this category is eliminating reviews by unqualified reviewers interested only in "easy money" who offer hyped reviews.A continuing challenge for all ratings firms is a self-selection bias in which a "tally of self-selected respondents is not scientifically reliable," and various firms have tried to solve this problem with different strategies.