Nycolas welcomed us, gave a tour of the flat as described in the ad, provided a useful map of florence and gave some tips about our visit. The flat, the bathroom and the room were clean, the balcony was very enjoyable to get our breakfast in the morning (great thing was to go to the local market litteraly 2min walk away, get some good food and enjoy it on the balcony!!) The flat is indeed very convenient to reach form the train station and is also very close to the very heart of Florence.
On the con side, the only thing I have to say is the room we had was on the street side where they hosted a street market every morning (a bit noisy) so not ideal if you intend to have a late sleep. Anyway, being a real tourist, you get up early to go ahead of the queue in museums!