If you have a lease you have the right to stay till the end of the lease. If you've been a tenant there for less than a year you are to be given 30 days notice, if you've been there over a year it is sixty days notice. Those numbers assume that you have no special disability or qualify for the age restrictions.
The type of housing and the age of the building also you live in also factor into the rights granted tenants by the law in San Francisco.
Be aware taht there are two sets of laws that govern your rights as a tenant. There are Eviction Laws and Rent Control laws, both are important. In other words knowing the rent control laws doesn't cover kowing the eviction laws. Rent control and some eviction controls vary by city or county while other eviction laws are state wide and can't be restricted locally.
As stated, cash does not move a tenant faster than purchasing a property with a loan. You will need to find out about the tenant's current status. Is there a lease in place or is it month to month? What is the age of the tenant? (some tenant's have protected status).
I would suggest you work with your Realtor to determine the nature of the tenancy and as suggested also contact the Rent Control Board. http://www.sfrb.org/
Doing your homework first will be important.
Hope that helps!
Alain Pinel Realtors
Read on line about tenant's rights, or call the rent board- all these are free, will give you a good starting point.
415 860 0765