Have been to Thessaloniki many times and slept in a variety of Airbnbs, but this one makes it definitely to the top of my list! Exceptionally clean, very well equipped, comfy, quite (very quite actually!) and it stays surprisingly cool, even in summer. Plus Tonia is an amazing host, who answers quickly and helps you with any issues you're having.
The only "downside" might be the not so popular location. The apartment is more in the B side of Thessaloniki but still situated centrally! Aristotelous square is reachable in only 15 minutes on foot. Being located in a less touristic area you find plenty of authentic and cheap restaurants nearby, some of them might be a real secret spot for tasty Greek food!