People are free to post whatever they want, it's the same as Steemit or any other platform. However, the problem you stated is explained in the whitepaper under 3.2. Submitted content is peer-reviewed to verify reliability and published on the platform:

Content submissions are not published on the platform before their reliability is
confirmed by a distributed consensus of peer reviewers. Every submission must also
meet certain criteria:

• It must refer to an actually existing place;
• It must not contradict publicly known facts regarding the place;
• It must be original (not plagiarized);
• It must not include unsolicited advertising (spam);
• It must not be slanderous or offensive