This doesn't seem correct to me as the way I understand how collections works is the collection agency now owns that debt. 

Having 3 furnaces and 3 hot water tanks would take up most of the room on the ground floor where I had a small one bedroom collecting much less rent if none at all.I would have to replace 3 boilers and 3 hot water tanks when it's time.

Just looking to collect my rent :-)Can anyone tell me what are the things which are different compared to the traditional residential lease in California?

You must collect the rent every month . 

It was clear to both parties, with email exchanges confirming that the end date is July 15th and that there will not be renewal of lease.However, I forgot to stop the automatic rent collection through Zillow, resulting in the tenant paying the full July rent on July 10th, which has already been transferred to my bank account.

Attempts to collect on it?

Rental portal to collect rent2.

If you have a lot of doors, any claims you're paying out (again, with your time spent dealing with issues) are generally offset by the premiums you're collecting from doors that don't require any or much attention.The fee structure should be transparent and easy to understand, and it certainly should be on the PMCs radar to avoid "project management" when possible. 

I collect 10% gross cash flow on each.

LindaMost statutes don’t allow you to collect double rent, the previous tenant would need to be pro-rated back for that portion of time you let the new tenants occupy.