It is clearly listed. There's little you can do about guests that don't a) read your listing or b) understand how AirBnB works. You could add a mention of the fee somewhere in your description, etc, but the kind of people who don't read it in the very explicit Pricing section aren't going to see it not matter where else you mention it.
The cleaning fee is not only easily apparent in the listing but is also included in the information that AirBnB shows the potential guest before they choose to book or request a pre-approval. Guests who don't "get" this are guests you don't want in the first place. They'll inevitably raise other ridiculous issues.