I have also encountered this in Spain, and my counter was to refuse the cash extortion after I had arrived and had the keys in hand. They will grumble or threaten you, but they know they can't force you to pay since it violates Airbnb policies. Even local occupancy taxes must be collected via the platform.

If they're extremely sneaky, their next trick is to fake property damage or extra cleaning fees collected post stay, but that's not a highly repeatable trick without them getting banned, so less likely to happen and you can dispute it with Airbnb, though ymmv.