When Wall Street firms began buying rental units in bulk in 2011, experts warned that they had no history of managing large numbers of rental properties spread over hundreds of square miles, and would skimp on costs at the expense of tenants. Now, according to the first survey on the practice, those fears are being realized. Tenants report that Blackstone’s rental management resembles that of a slumlord. They rent properties with significant maintenance problems, fail to keep contact with their customers, and violate state and local laws.