Appartement is as described: small, dark, in a calm narrow street, clean (but some spider web in the ceiling), location is great. It's affordable for Venice, so expect to get what you paid for.
The supermarket Despar is close by, think of stopping by to get some basic stuff like soap for the shower, shampoo, sugar for your coffee. Some toilet paper is provided, but if you stay for more then 2-3 nights, you have to get more.
The worst is the Wifi: not reliable most of the time in the morning or at night (working a little better after midnight). So if you don't have an italian sim card or can't use yours internationally without expensive costs, then it's very frustrating. Bed is confortable, but the bedsheets are very used, it's inconfortable for sensitive skin. It was a little smelly when I arrived: you can't open the window in the room for some fresh air, there is no screen against mosquitos. The window in the kitchen has a screen but the fit is not good so mosquitos get in anyway.
And yes, they request more money for a touristic tax, cash, at the end of the stay. It's mentioned in the ad and I checked with Airbnb: it's very annoying that it's not included in the price but they can do that, so think of keeping some Euro to pay it (it's 3EURO per night for the first 5 nights, and I think it's per person too)