Inconsistent behaviour towards customers

Builders Warehouse is running a promotion involving a competition where customers hold onto 40 litres of paint for a period of 10 minutes which I have been a witness to and my husband, a participant. Three weeks ago my husband participated and held the 40 litres of paint until the thin plastic handles cut into the palms of his hand and slid off just before the required 10 minutes. We also watched the other participants in the consecutive weeks, none were able to contain the paint handles in their hands. However, yesterday, the promoter said to a customer who also FAILED to hold the paint, \You look like a COOL guy so you may have the voucher anyway"I approached him about being inconsistent and giving one person a voucher and not the others that put equal effort into the competition which is not the simplest or painless! I advised him that this was not ethical as how does he distinguish a \""COOL\"" participant from the others"