My fiance and I came to Porto for a few days on the back end of a European vacation. We chose it because neither of us had any clue what to expect, only hearing great things about a cultural, historical city on the water.
We booked with Mario in part because of the location and proximity to restaurants/bars/touristy spots in Porto, and in part because of the affordability. Upon arrival, the location of check in was a little tough to find (addresses and house #s aren't super prominent in this area) but Mario was very quick to respond to our messages for help. He wasn't able to be there, but had a colleague, Rafael, check us in instead. Not only did he walk us to the apartment, show us all the amenities, he also pulled out a map and offered suggestions on where to go and what to see in the few days we had.
We took their advice on locations and had an unbelievable stay while we were there. It was fun to do the touristy stuff, but we mostly stayed near the local spots Rafael recommended and were blown away.
Our flight was 7 hours after the check out time, and Mario let us leave our bags at the apartment so we didn't have to pay for a locker near by.
Our experience was exponentially better because of Mario, Rafael, and AirBNB. Would recommend staying here to anybody who asked.