How tight is San Francisco’s housing market? So tight that the landlord of a rent controlled apartment building at 312 Fillmore Street has sent a memo to his existing tenants, telling them they must show they have an annual income of at least $100,000 and a FICO credit score of at least 725.Or else...what? The memo (which describes itself as “informational”) doesn't say. When ABC News phoned landlord Robert Shelton to ask, he hung up. When an ABC News reporter knocked on his door, Shelton slammed it in his face.Local housing and tenants’ rights experts tell ABC News they are in no doubt what such memos are meant to accomplish: They’re supposed to scare the heck out of tenants, on the chance that ones unaware of their rights will vacate.