My girlfriend worked for a small-ish company (less than 100 employees) that got ONE negative review on Glassdoor. The company executives were so angry about it that they contacted Glassdoor, trying to get them to remove it. Denied. Then they hired an attorney to try and force Glassdoor to remove the negative review. Denied again. Finally, a few weeks later, someone from Glassdoor reached out about some sort of premier program for employers. Nothing was ever stated directly, but it was implied that reviews would be "managed" with the premier program. They signed up. Negative review disappeared later that day.

I don't know the details about the "premier program", like what it was specifically called, but the negative review did magically disappear. Also, everything said in the negative review was totally true.