This is just one of the many scams of Air Asia. You'd have to pre-book your checked-in luggage and you'd better know how heavy it's going to be. Recently was at the horrible Kuala Lumpur low-cost terminal and because my luggage weighed 5 kilos beyond what I had booked for (some last-minute shopping) they demanded RM50 per kilo, which would come up to RM250 (US$85), which is more than the air fare (to Bangkok) itself!! I turned away and repacked my things into my hand luggage. Since the whole terminal is in a huge mess, with everyone pushing, shoving and shouting, they didn't notice or care what I was doing behind their backs. The terminal is way under-staffed and on the tarmac I almost walked up the wrong plane, as there were no signs. Multiple lines of people trying to find and get up their plane. Malaysia Airlines offers 30 kg free checked-in luggage for economy class. And the main KLIA terminal is paradise compared to the fish market of an LCCT.