To be honest, these people sound like shitty, lazy landlords who deserve their bad tenants. They
1 - didn't do a reference check;
2 - didn't swing by occasionally (even every couple months) to verify the condition of their property;
3 - were renting property out and hadn't bothered to provide neighbors their contact info in case of problems;
4 - quite possibly (this is highly variable / city by city) hadn't notified the city they were renting these units, or the city would have sent the fines to them rather than (presumably) to the tenants.
(I say this as a landlord). They feel they are entitled to take out a mortgage then collect checks without any work. It isn't that easy...