A yelp review of a San Francisco landlord's offerings form the basis for a defamation claim according to the California Court of Appeals. Referring to the landlord as a "sociopathic narcissist" is not actionable as a statement of opinion. But alleging:
Of the 16 mostly-long-term tenants who lived in the Building when the new owners moved in, the new owners’ noise, intrusions, and other abhorrent behaviors (likely) contributed to the death of three tenants (Pat, Mary, & John), and the departure of eight more (units 1001, 902, 802, 801, 702, 701, 602, 502) in very short order.
is probably factual. And since two of three allegedly deceased persons were still alive, the statements were false.
Here is an explanation, some advice and some marketing of legal services around the issue of internet defamation: