My wife and I had a perfect stay in Venice at Isabella's Airbnb! The location is amazing! Just steps away from St mark's Square, yet far enough from the noise and crowds.
The apartment is very close to Vaporetto stops. Isabella met us right at the stop and got us settled into the apartment.
As others have mentioned, the lift (elevator) is up a few flights of stairs, just be aware that you will have to carry your luggage to the lift (not uncommon in Italy).
I would highly recommend Isabella and her Airbnb to anyone traveling to Venice!