When we showed up at the place, there were just 3 beds - a double bed in one room and a single bed in another.
Mind you, this being carnival season and stuff, we were paying a handsome amount for our rental. However, when we got in touch with the host (he lives in the US with his wife, a care taker opened the house for us..) he refused to acknowledge the issue. He said: "There's a couch in the living room, one of you can sleep there - that way the house accommodates 4 people".
So we got in touch with AirBNB support who said they would find us another place. Of course they couldn't - everything is sold out during carnival. So, they finally decided to refund the "AirBNB fee" to us (about USD 54) so that we could use it to buy an inflatable mattress to put on the floor.
I asked them why they couldn't give us a full refund considering this was absolutely unacceptable as they should take responsibility for incorrect listings that lead to situations like this. (for what it's worth, Expedia, etc. have a far higher standard of customer service when it comes to stuff like this) They replied saying that the host had already been paid out - as if that's our problem.. =/
Anyway, we had no choice but to stay so we did indeed buy an inflatable mattress... AirBNB's customer support however was pretty terrible and the host was a complete asshole to us.