Here is some practical advice for checking out a rental situation and not getting screwed.
Rental agent:
If you are renting from a rental agent, look them up at http://www2.dre.ca.gov/PublicASP/pplinfo.asp If it is a big company, and you have just some temp as your point of contact, look up the company on that site.
Unlicensed/informal agent:
If it is an informal rental agent (like the dude helping you says he is just a friend or something), ask to see something (like an agreement) showing that he is authorized to find a renter and have him show you his ID. Then check to see that the names match (see below for ownership look up). This is less important with licensed agents since their info is public record.
Owner:
If it is an owner who is your contact, check the ownership records with the county recorder website or ask a Realtor to look it up.