Can companies delete and manipulate Glassdoor reviews?

I get a weekly digest of employee reviews for my company, and very often I've observed that the negative ones are deleted(clicking on the 'read more' section gets me to an error page).

Apart from this, slice is actively putting up fake one-line reviews to save their sinking reputation.

Highly unethical on part of slice. I wonder how Glassdoor is even allowing this.