I have used website promotion services from SEO specialists not so long ago and I want to make sure that the work was successful. Can you tell me how to check on-page SEO on a website? Are there any tools for this?

Yes, of course, you can do a check with this on-page SEO checker - pr-cy.io/tools/content-analysis/ (https://pr-cy.io/tools/content-analysis/). With its assistance, you will be able to find out all the necessary info to determine the effectiveness of a particular advertising campaign. In addition, with its help you can check not only your site, but also the sites of your competitors, which is also very useful in promotion.