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Research-integrity watchers had already suspected that citations are for sale at paper mills, services that churn out low-quality studies and sell authorship slots on already-accepted papers, says Cyril Labbé, a computer scientist at Grenoble Alpes University in France. “Paper mills have the ability to insert citations into papers that they are selling,” he says. In November 2023, analytics firm Clarivate in Philadelphia, Pennsylvania, excluded more than 1,000 researchers from its annual list of highly cited researchers because of fears of citation gaming and ‘hyper-publishing’.