What is the ruling on working as a broker in e-marketing to increase positive product reviews, where products are given away for free to buyers in exchange for their positive review, and the broker receives a commission for each review?

This type of marketing is impermissible because it involves deceiving buyers and creating the illusion that the positive review is genuine, when in fact it has been bought with money. Islamic law has forbidden such deception and illusion, just as it has forbidden najash (artificial bidding), based on the Prophet's (peace be upon him) saying: "Do not meet the riders (to buy their goods before they reach the market), and let no one sell over the sale of his brother, and do not practice najash." And his saying: "Deceit and trickery are in the Fire." A review is a testimony, and it is not permissible to take a fee for a truthful testimony. If it is a false testimony, then it is a lie and unlawful acquisition of wealth. Therefore, one must fear Allah and beware of unlawful earnings.