my own real life experience

We rented a 2br apt in a 4-plex when we first moved here. The landlord charges about 10% below the market. Tenants: 1. young professional couple without kid (us); 2. a single lawyer lived there for over 10 years; 3. a single IT guy, also at least 3 years when we moved in; 4. corporate housing for a company which is empty most of the time. Everyone was very nice, quite and resonsible. We stayed for 2 years until the landlord retired. Then he started to hike up the rent to market value, maybe a bit above even, within half year, all three of us bought our own houses and moved out. Last time I heard, the single mom with 2 teen boys gave the landlord a lot of headache. The big noise/bad neighbor leads to more bad tenants. The turn over rate was half year or so.