Some people are well-trusted in their personal or professional domain with a lot of fans following their public media. If your message deals with a related topic, you have an appropriate opportunity to send them a marketing request, usually in the form of a paid product review or conventional advertisement. The right way to manage this is to affirm that you want to preserve the integrity of the trusted individual, especially in the case of a product review. You can offer to ship them the product free of charge and have them evaluate it (sometimes with a small up-front payment for their time). Then if they could genuinely endorse it they would make a review for a pre-determined compensation amount. If they cannot, they may tell you their reasons, then either oblige to a second shipment or decline further correspondence.