We rented an apartment from www.bairrus.com Juan Batista was very helpful. Our flight was late arriving in Lisbon and we communicated via facebook messenger (no wireless cell plan in Eurpoe) as there was wifi available almost everywhere, some times for a minimal fee. The apartment was in a great location. Restaurant row was right there and very close to the metro station to get to Sintra. Short walking distance to the water front square.
Juan got us settled in. Answered our questions and even gave us a treat. The apartment was modern and had everything that we needed. We were in Europe late August/early Sept and had no problems with not having airconditioning. It was cool in the evenings and there was a fan.
There were many steep stairs to get to the apartment and we had a lot of luggage. But we managed. Everything in Lisbon is on a hill :)