Me and my girlfriend stayed at Carlo's place for two weeks in February, in order to work in Bologna. I've been to Bologna five times now, and it's become one of my favourite cities, beautiful architecture, super nice people, perfect climate - and gentrification hasn't hurt its charm yet.
Carlo's flat is located really close to the centre, everything is in walking distance. It's a beautiful, quiet neighbourhood. The flat has everything you need, everything is clean and the bed is comfortable. It is rather dark though with no sunlight coming in (which is not Carlo's fault, of course), so if that's important to you, you should consider it.
We never met Carlo, the flat has a code lock, which makes checking in and out simple (and you can't forget your keys), but we stayed in contact via Whatsapp, and he seemed very nice and was always quick to answer. He also sent someone to clean the room after one week and exchange the towels, great!
Wireless internet is fast, the gas stove works great. The shower is okay, if not a bit on the short side (I'm 180cm, so not a giant, and I had to bend down a bit).
There was one thing which wasn't ideal though: In the beginning, the shower didn't stay warm for longer than 10 seconds, switching back and forth between hot and cold. Also, the room was rather cold (~18° degrees) for the first 3-4 days. There were easy fixes and I wouldn't mention it normally, but instead of just telling us how to fix the problems, Carlo would first tell us to "not use the sink when the other person is in the shower" or to "not open the windows if you want to stay warm". We found that to be a bit degrading because - of course - we didn't do those obvious things. Only later, after we asked again, he would tell us how to keep the water warm and to raise the temperature, which was very easy to do.
But, all in all, that's the only criticism we had, and we would still recommend coming to Carlo's place in Bologna. Thank you, Carlo!