Influencer marketing should be very much an open dialogue between brands and influencers. Brands will sacrifice their tone of voice to that of the influencer, and in turn the influencer will communicate your brand/product positively, in an authentic and creative way that connects with their followers and fits in with their regular content.
It has a lot to do with trust, but with direction (particularly relating to what you want to achieve) you can establish a good working relationship. Whilst brands entrust an influencer to create the content, brands can certainly set specific guidelines.
Tip - If you have concerns about the content creation process, as part of your agreement as a brand, you could perhaps request to approve the draft content before it is published by the influencer, so that you can suggest small changes if anything is unsuitable.