I have stayed at many Airbnb rentals before and was never asked for additional fees after paying for the booking via Airbnb. I arrived late night and was told that I needed to pay additional amount in cash which I didn't have on me. The next day I emailed Airbnb to find out whether this was a legitimate request. They told me that it was against their rules to pay additional fees, so I passed that info to Nicole. Later, Airbnb got in touch with me to tell me that under certain circumstances they do allow that. As soon as I heard that, I paid the landlord the full requested amount in cash.
One thing I was uncomfortable with was that Nicole called me multiple times after 10pm to chase down the cash deposit. I'd much rather just pay the entire fee at the moment of booking on the site.