I stayed with my friend for 4 nights in Christian's apartment and I could not recommend it enough.
From the outset communication with Christian over air bnb was great and replies were instant. When we arrived we met Mercedes (his sister), who showed us around the apartment and had left us oranges, olive oil and a couple of chocolate ice creams which was a lovely touch. She was incredibly helpful over whatsapp during our stay - replying instantly with great recommendations.
The apartment itself is clean, spacious and finished to a high standard. We had everything we needed and the TV had chrome cast so we could listen to spotify and watch netflix which was great for the evenings. The flat is ideally located in the old town, extremely close to the central market, monuments and shops. There were plenty of shops and restaurants nearby, but next to the apartment is a great bar called Leipzig bar. The owner was so friendly and did amazing margaritas and also gave great recommendations.
Valencia is well worth a visit - beautiful old town, the beach, the city of arts and sciences, great nightlife, great food...and you'd be hard pressed to find anywhere better to stay than Christian's apartment!