We spent two nights in mid Sept at this very affordable, one bedroom apt that was conveniently located close to Piazza del Campo and within walk distances from the bus station.
One of my challenges was getting in touch with the owner. I've emailed the owner multiple times, once with Expedia's help, and not a single response. I had to request a staff member from a tour company to contact her by phone and she finally responded to that staff member on her second attempt. I also attempted to arrange a check-in time a couple days prior to arrival and she finally called me back after numerous attempts.
Her brother was punctual in dropping off the keys to us.
The one bedroom was not equipped with AC, at least not accessible when we were there in mid Sept. Fans were available but not sufficient to allow enough air flow. Apartment was not equipped with paper towels or any toiletry aside from toilet paper. Floors were not very clean. There was a separate bed in the loft which my daughter did thoroughly enjoyed.
I would only recommend this one bedroom if you're looking for an affordable, spacious place that is close to Piazza del Campo.