Asalam-o-Alykum
Brother, Swift DLX is an excellent car but not fuel efficient, I've measured average once after purchase and it was 8.5 km/l on 135 km drive, despite of light foot. I will again measure it on 400 km drive then can give you exact average.
No specification required during check up, one you are satisfied with engine and exterior body get its suspension, jumps checked from some good mechanic before taking decision or use pak wheel inspection which I missed.