Marco, Alice, and their daughter Nina, who turned four while we were there, were very cordial and very helpful with restaurant recommendations and train reservations. Their English is very good, and they also speak French and perhaps other languages. The neighborhood is quiet and non-commercial, but is only a five minute walk from Piazza San Marco and the vaporetto stations.
We rented an apartment, which had a small kitchen, and a grocery store a one minute walk away enabled us to do some cooking at home.
I would caution prospective guests that B&B San Marco requires walking up four flights of stairs, but is well worth it.