The operators usually victimised those that orders for the whole group. They might overcharge as there may be some customers that fight for the bill and when this happens, they won't scrutinise the bill. Remember those days in Old Klang Road seafood restaurants (at the junction of Taman Desa). You fight for the bill and then suddenly you are overcharged RM10 to RM15 and sometimes a pack of Marlboro is inserted in the bill.

Happens nowadays, in Chee Xiang, 11th mile Cheras, I ordered a quarter duck and 'char siew + siew yoke' and three rice. Asked for the bill and it was RM46.00, I paid it and then did the maths as it was itemised and I was overcharged RM10.00. My wife went back and ask the 'see tow porr' to calculate again and she just opens the drawer and flash out ten bucks and returned it to my wife without looking and apologised. So, it proves that it is pre-meditated.
Just go back to ordering single orders. Two ask for 'duck thigh', two orders 'char siew', and two orders 'siew yoke and when the food comes, push all the meat into the centre of the table. Total, usually RM36.00 for all plus rice

If you orders for all, the bill might come to over RM50.00 to RM60.00 plus rice. The former set up still leaves a lot of money to re order and re order again. Or maybe add two more double boiled soup and a green, it should be enough for six anyway. Might look cheapskate but then they were the unscrupulous ones.