Seller with tenants but NO lease in place...

Hello BP World,

I have an interesting situation.  I am looking at a property that is not under rent control.  There is a tenant, but the home owner and the tenant never put a lease or rental agreement in place. The tenant has been paying rent for many years. This property is located in Oakland CA. 

I am assuming that at the point which I close, I have the open option to either evict the existing tenant or offer them an actual lease.  

I am just wondering if anybody sees any potential problems with getting this person out, besides a standard eviction process.

Thanks in advance,

Arlen