This is the method I used to get our first 5,000 monthly paying customers and about $75,000 in MRR. Not all of the reviews were completely free. Occasionally, the influencer really liked our product, and she was a perfect fit, but she would ask for a small compensation of $50-$150. Back then it was the maximum budget we could afford, and we paid.
Just make sure that the reviewer discloses that he or she was compensated for the review. Otherwise, you could land into hot water with the FTC.
FTC position: “While decisions will be reached on a case-by-case basis, the online post by a person connected to the seller, or someone who receives cash or in-kind payment to review a product or service, should disclose the material connection the reviewer shares with the seller of the product or service.”