We can't blame McDonald's though. In their advertisements all over the world, they'd already put on a disclaimer. That smaller-than-flea disclaimer on their ads. Anyone with supervision could've spotted it.
The art of packaging is not only used by big companies but also applied in simple businesse; k lah, let's make an example out of local fruits:
In Pasar Malams, you could easily spot fruits in perfect condition on baskets with a price tag; RM5 sekilo. When you ask the pakcik for a kilo, he will shove his hands deep into the basket and fill half of the plastic bag with rotting fruits, the other half with the good ones lah.
As widespread as it is, cheating, no matter how you do it is wrong. It's just is. It'll cause multiple problems to consumers and....... let me put it simply, in a term anyone of all religion could understand:
With CHEATING, NOW ANYONE CAN GO TO HELL!