In theory, a paid editor has to report about paid editing and who is a client on the article talk page or in his or her user talk page.
In fact, nobody does it either in Ukrainian, nor in Russian Wikipedia, and only a little in English. For example, in Ukrainian wiki, less than 10 editors have marked themselves to receive payments, and there are even less articles which include the paid editing template.
Nobody does this because the majority of the editors in the community and the Wikimedia Foundation are fighting with even the smallest mentions of paid contributions. Edits are cancelled, the articles are removed, and the editors are blocked. As soon as the article is designated as a "paid", it falls under the attention of a dozen wikipedists and the chances of survival are literally equal to zero.
It includes ideological differences, moments of envy (somebody writes for free and some editors are paid), and sometimes even conflicts of interest appear due to work of competitors. So now there is a toxic environment for paid contributions to Wikipedia. And the best way is to use confidential editing services.