Merce & Jepis's place was easy to find from the plaza, and provided a great central place to stay and find your way around Barcelona! Their place is in an old building with a small elevator, but the apartment was nice, comfortable, and clean. The balcony was very nice as well, and although is was near the center, it was quiet in the apartment at night. It was also easy to get around on public transportation from the apartment, a park across the street, and there were nice places to have breakfast within a 10 minute walk.
My only criticism is that we were asked to pay additional fees in cash upon arrival. We were aware that we would need to pay taxes separately in euros when we arrived, the total for this was about 13 euros. We were informed the day we arrived that there was an additional charge for "late arrival". This charges range from 25-50 euros depending on how late you are. Check in is at 3pm, we arrived at 9pm, falling in the 1-8 hour late category, which incurred a 25 euro fee, and we did not get a receipt for this charge. Although the check-in was excellent, and we were given a lot of great local tips, I would have been more comfortable making additional payments through the Airbnb website.