You don’t ask people to speak how you want, you simply only invite people who already have a history of speaking how you want. This phenomena is explained in detail I. Noam Chomsky’s work around mass media (eg NY Times doesn’t tell their editors what to do exactly, but only hire editors who already want to say what NY Times wants, or have a certain world view). The same can be applied to social media reviews. Invite the person who gives glowing reviews all the time.