What is the ruling on purchasing accredited professional certificates from official bodies, which are issued by educational institutions for a fee to professionals who do not possess documents proving their experience, and what is the ruling on working in their sale?

If the certificate includes forgery, falsehood, or fraud, then it is a false testimony (shahadat az-zur), and it is not permissible to obtain it. However, if it is free from these prohibitions, then the fact that it is for a financial consideration does not affect the permissibility of obtaining it.