Depends on the country, but usually a “background check” is nothing more than paying a lawyer to check if you have ever been convicted, accused or investigated for a crime. Prosecutors have an archive and a office of records to collect and share that public information. This is why clearing records are important in courts and settlements. It’s a big mark to say the person is actually alright and won’t be found in the records if searched, as they were cleared. Other than that it is usually just a phone call to a previous employer to ask if you were an asshole there.