How much is Impact Factor worth?

The purpose of this work is to present an aspect of counting citations, which is correlated to the Impact Factor, very important for journals in scientific communication, and provides information about the position of a scientific journal in a particular research area. Sometimes citations don't count in a research output, e.g. if an article is published in a predatory journal. Those journals are not indexed in Scopus and Web of Science. However, an offer to pay for citations can concern high quality journals and no algorithm would be able to catch that. An example of a letter with an offer to buy citations illustrates and raises awareness of that practice.