Being a financial consultant and accountant, I always have a nag about the price manufilation that is being done, in careful manner.
Would like to give one example of it. More likely than not, the promotion is usually not in the best of the customer. Either the expiry date of one additional item is nearing the maturity date or one additional gift item cost is so taken from the end customer in a manner that the customer think he has a good deal.
The tip to catch such is always calculate how much is each per liter/kg cost.
In the below case, normally the more you buy the better it should be. However, I calculate that smaller package is more cost effective than the larger pack.
The different pack price per Sq meter from smaller to bigger are 5, 7.33 and 7.45
Shows the better option is not in bulk but in smaller quantity, normally is the other way.
Be smart in shopping! 
