We stayed 3 days in Stelios' apartment and really enjoyed this time. Location is very well, a few minutes from the main attractions. 2 supermarkets, bakery are within 2 minutes walking.
We didn't meet Stelios but contact was very fast, he gave us a few tips, informed about some difficulties with public transportation.
I can't complain about anything and recommend this place to stay when visiting Thessaloniki :)