It was bound to happen at some point and it did in Lisbon: I had my first negative experience on AirBnB. While the flat's location is superb and the price attractive, I cannot recommend this accommodation. What went wrong (in a nutshell):

Arrival - I have been communicating with Vitor for weeks before my trip and gave him a lot of details on when and how we would reach Lisbon. We agreed I should call him a couple of minutes before arriving at the flat, having given him a rough time estimate. Long story short, his mobile was off and it took me an hour to be able to reach his mom, who had to fill in for him as he travelled to Brussels that day. It turned out that Vitor had sent me an e-mail 17 hours before explaining he wouldn't be available. Well, I guess he forgot that people on holidays are not able or not willing to check their messages all the time. At the end, we waited for over 1,5 hour with our luggage on the street before getting in the flat. Not a great start.

Cleanliness - That is by far the worst aspect of the flat. Sheets and blankets had massive stains. Cupboards smelled funny (dusty!). Cutlery and glasses were greasy. Even not being particularly fussy about it, I must say the overall cleanliness was very lacking indeed.

Miscellaneous - The other things that accounted for a negative experience were: a tiny TV, a claustrophobic shower and an incredibly noisy bed. That is to say, you wake yourself up every time you move at night, then you have a movement-free shower in the morning and cannot even sit back and relax in the evening because you can't see anything on the screen.

To sum up: the entire street is filled with AirBnB offers and there are good chances you will find a better deal elsewhere.