We stayed at Marco's place in May 2018.
Pros: The flat is nicely furnished and has a decent amount of space (full bathroom, bedroom, kitchenette, and entryway). It is also pretty central, just a 5-minute walk from the Ponte Rialto. Marco provided us a bottle of Prosecco after we checked in which was a nice touch. He was also responsive via email in advance of our stay.
Cons: The flat is rather hard to find. Marco emailed directions in advance, but it is still tucked in a very narrow alley. We relied on a combination of Google Maps and his photos. While the listing says self check-in, we did have to meet Marco in-person to get the keys, so this was confusing. Marco was rather quiet and it made the whole process sort of uncomfortable. Also, the flat seemed to be pretty pricey. For the price, I would have expected better A/C (for example, the unit in the bedroom and not the hallway), and more nice touches like washcloths, small toiletries, etc.
Overall: Good choice for staying in Venice, but I am curious if I could have found a better spot for the cost if I had booked earlier.