Questionable publications have been accused of greedy practices; however, their influence on academia has not been gauged. Here, we probe the impact of questionable publications through a systematic and comprehensive analysis with various participants from academia and compare the results with those of their unaccused counterparts using billions of citation records, including liaisons, e.g., journals and publishers, and prosumers, e.g., authors. The analysis reveals that questionable publications embellished their citation scores by attributing publisher-level self-citations to their journals while also controlling the journal-level self-citations to circumvent the evaluation of journal-indexing services. This approach makes it difficult to detect malpractice by conventional journal-level metrics. We propose journal-publisher-hybrid metric that help detect malpractice. We also demonstrate that the questionable publications had a weaker disruptiveness and influence than their counterparts. This indicates the negative effect of suspicious publishers in the academia. The findings provide a basis for actionable policy making against questionable publications.