Hi.

If he puts the quantity which is to be sold in the pan whose arm is of larger length. He would gain...this is because torque of mg on that pan would be more than the torque of mg on the other arm (due to unequal arms)....so the weight shown is wrong and is more than the actual weight .However if he puts  the WEIGHT on the pan having larger am length he would be

at loss due to the same reason.So maybe the answer is both A,B