The flat was well-equipped, clean, warm, perfectly located in between old and new town (and right next to a street market). Our host, as others have mentioned, was exceptional. Giving us really thoughtful recommendations and tips based on our preferences and his deep knowledge of the city and all its ins and outs. He was extremely easy to communicate with, available and made our stay a hundred times better than it might have otherwise been.
We would definitely opt for Riccardo's flat if we're ever in Bergamo again.
The only small note I do have is that there isn't self-check in but with such a flexible host there is hardly any need for it.