Some weeks ago a company contacted me via email. In summary, they offer to pay you if you include a co-author. They also need you to sign an agreement with your University and them. So, from one side, it seems kind of legal (since in the agreement they state “sponsorship”), but from the other side, these practices, I am afraid could lead to unexpected retractions, due to the likely unethical side of the business.
Is this kind of service illegal or unethical?