If you can see the agent's name, you might consider looking up the agent's information up on the California BRE (Bureau of Real Estate) website to see if the person is a real agent.
Even then, if you think it is too good to be true, it probably is. Be very careful; there are a lot of scammers out there. Proceed with caution.
Find a licensed agent you trust to show you properties that you can enter, check out for yourself, and research with your agent. Protect yourself.
Trulia and other sites are inundated with scam rental listings, so you are right to be skeptical. If the landlord is out of state or the country and will send you keys when they cash your check, don't send it. Only trust people you can see and talk to in person, either the owner or their licensed agent.