If you’re flying within China, elong.com and ctrip.com are the websites to use to get the best prices. However if you use their English sites, you’ll see fewer flights and be charged more. For example, on the English site today a search for a flight from Beijing to Shanghai yielded the lowest fare as 660 rmb going and 560 rmb back, but the lowest fare if you used the Chinese page was 490 rmb going and 390 rmb back with ctrip. This is for flying on the very same airplane.
Ctrip showed the cheapest fare from Beiling to Tokyo as 3840 each way and If you used their Chinese page each leg cost 2800. In this case you could fly on carriers that didn’t even show up on the English search. For a round trip ticket, those who use the English page pay $337 more.
I tried to compare with elong.com, but today the server’s down.