My boyfriend and I stayed three nights at Juan's house and Juan is a very friendly and attentive host, asking frequently if everything's ok and even sharing a beer and his dinner with us on our last night! We also had to change the reservation at the last minute and he proved very understanding and kind. If you don't speak Spanish, communication may be a little challenging, but as Juan spoke a bit of French and English as well, we made it.
The flat is absolutely ideally located in a very quiet street 2min away from the city center, in a very typical and picturesque neighborhood. It's a pleasure to walk around.
About the room and the house itself, it's as charming as on the pictures, but darker (as most of the shutters are closed the whole day to keep the house cool) and the only down point to our otherwise very comfortable stay (the bathroom is perfect, the kitchen convenient and the terrace really nice) is really the bedding, which could be improved. We didn't look very carefully at the pictures, so for other distracted users it may be good to know that this not a double bed but two single beds. The mattresses are very old and you can feel most of the springs. The sheets we had were clean, but very old as well. I don't say it prevented us from sleeping, but it has to be mentioned. And as a last detail, the room and the one beneath both have old French windows on the patio (as you can see on the pictures), so soundproofing and intimacy are not always the best.

I would definitely recommend Juan's house for its charm, the location and Juan himself, but the beds could be a little more up to the standard of the decoration. Very good value for budget travelers to feel a real Sevillian atmosphere, though.