Be sure to find out if your carrier will an LLC as a named insured

Make sure you find an insurance carrier that knows you will be doing AirBnB as well

At United Assurance we implement a strategy that leverages our relationship and understanding of the carrier to get the best of what the market is dictating.

I agree with @Greg Carrier .

Personal Insurance carriers can be resistant to add a landlord as an additional insured and would likely make an additional charge for doing so (could be significant).  

I'm curious which insurance carriers are mostly used or considered for properties in California particularly.  

As someone in the insurance industry and specifically in loss prevention, yes, this is fairly common for standard carriers and also not unreasonable.

I can't imagine an insurance carrier covering a landlord under these circumstances, if they did I would think they would need to be informed of what's going on and agree to it, and with a higher premium for that risky time period.

Own properties in 6 states and have individual policies on each unit with one of the big national insurance carriers.  

Also, it's preferable to beat up on the other insurance carrier instead of souring the relationship with your own carrier.An independent adjuster usually charges 10%-15% of the total payout as payment.