The flat is really far outside of the Lisbon city centre, the pictures are way too good for what you finally find. Personally I was told to rate at least 4 stars because this is essential for the income of the host. He was friendly overall, but we did not feel comfortable as himself and his wife are right next door, and the flat is really not in a good shape. I do recommend to go s bit closer to the City Center and if you are travelling on budget, look for hostels in the city centre, otherwise it will take you at least a 30 minute walk.
I did rate this so low because I felt pushed by the host to give a good rating which I never had been asked before, as well as mould in the bathroom, and an overall bad smell.