I spent 5 nights at Guido's home and my experience couldn't have been better.
It's well located, nearest vaporetto spot is like less than 10 min walk, but you can walk everywhere from there. The apartment itself looks like a tiny personal museum with lots of pieces of art as decoration - loved it!
As other reviews mentioned, the room's window face a busy and popular square, so it's noisy during the night, but a pair of earplugs solved my problem.
Guido would also check from time to time if everything was ok and give local tips!
Will definitely stay there again when I'm back in Venice.