Stay at Sergio's flat was wonderful. Flat is quite renovated and has everything one may need and even more (towels, kitchen utilities, shampoo, etc.).
Its location is great (very close to metro), and, frankly speaking, there is no need to use public transport very often, you can reach any sightseeing on foot (sea, Passeig de Gracia, Park Guel, etc).
Communication with Sergio was OK, he is very responsive and helpful.
We had some problems with washing machine, we were not able to wash our clothes for some reasons but it did not spoil our staying. Sergio did repairing but we were afraid of touching it one more time, so did not wash)))
Also flat has quite old windows that face noisy street with very heavy traffic, so if you have problems with sleep, bring ear stoppers or just get used to noise.
And one more thing: as central heating is not common to Barcelona in general and Sergio's flat has old windows it was quite cold inside when it is just 10 degrees of warmth outside. But Sergio provides good-quality heaters and they survive us at night. Thanks a lot.
We will recommend this flat to our friends and have nothing against visiting it again.