We had a great stay at Posada, for a week in June 2017. We were 4 girls.
Posada is a very calm little village 40 minutes drive from Olbia airport. The village itself is extremely quiet, not a lot to do, but that was exactly what we were looking for. If you want a lively place, I would not suggest going there.
Communication with Giulia was very easy. Instructions on how to arrive were also clear. Once we arrived we met Graziela, a lovely Italian lady who met us at the house and explained everything to us (she lives 100m away, so it was really easy to get in touch during our stay, whenever we had a question).
The house itself is nice. Don't expect luxury, but it's very well equipped with everything you need for your stay. The point I had not realised when booking it, (not sure if it was mentioned in the description or not), is that it is a 3-storey house: downstairs you have the kitchen and a beautiful balcony with sea-side and country-side views, then the living room on the ground floor, and the 2 bedrooms and bathroom upstairs. The stairs to go up are extremely steep, not suitable at all for older people or young children. Even us, that are in our 30s, were extremely careful when going up and down. We were constantly getting our flip-flops off to go up and down, as it was so dangerous.
The rest of the house was ok, rustic but nice and functional. There is obviously no AC (and no fans either), but at night the breeze coming in from the windows was nice enough to sleep well. There were no mosquitoes so did not have any bug-issues. The kitchen works well, it has a small stove and electric oven. The bathroom is big, however the shower space itself is really small, therefore it was quite tricky not getting the whole floor wet during the shower. However with a bit of attention we managed to do it.
Only the last morning we woke up and had no water, but we did not even had to call Graziela, she came proactively and solved the problem in less than a minute!
We were also allowed to stay until later the day that we were leaving, allowing us to enjoy half a day in the beach and then taking showers and doing the check-out at 5pm, which was really kind and helpful.
I would recommend staying in this flat, just see if the comments above are ok for the kind of holiday you are expecting.
Thanks to Giulia and Graziela for a very nice holiday!