Fantastic apartment! real state of the art in the heart of Venice. You cannot find any better. Don't let the silliness of asking 100 euro cash on the side deter you from booking it. It makes people feel part of a shady dealing but apt is well worth the full price with the 100 included. Nickel and dime you with the tassa di soggiorno to be paid in cash upon arrival when you are spending hundreds of euro also denotes a lack of touch.
Another minor issue was that an agency is not the same as an owner who would know his apartment intimately. They did not know exactly how things work.
All in all though this is a real gem, although not cheap, and likely your best apt of your Italian vacation.