I stayed 3 nights at B&B Sant'Agostino in June. Roberto was very quick to reply to my email enquiry, which was appreciated.The flat was clean, well maintained and had all the basic amenities needed for a short stay in Genoa (including free wifi). The B&B offered privacy since the owners do not live there themselves and was amazing value for money. The location is perfect, only a 5 minute walk to Piazza Ferrari and 10-15 minutes' walk to the Aquario. Roberto was super friendly and helpful. Also worth having a meal at the downstairs restaurant, la Forchetta Curiosa, which served really nice food.
Do take Roberto's phone number prior to arriving so you can get in touch if there's no one around when you arrive (which happened to me)!