Is a person's purchase from a website via their own marketing link, and obtaining a commission from their own purchases without marketing for the website, considered a legitimate act or not?

It is not permissible for a marketer to make a purchase through their own link to earn a commission, as this defeats the purpose of the website and violates its terms. Contracts and conditions must be fulfilled. As for the money obtained through this method, which cannot be returned, it may be given as charity to absolve oneself of responsibility.