Because it's Christmas time, and because we love these at our house, let's take a look at Turtles. There was a time, not so long ago, when a box of Turtles was a box of Turtles - everyone had the same size and packaging. These ads are all from local flyers from the first week of December.
Note the different sizes and pricing. Pricing is an art, and sometimes certain strategies work, however liberal deception can come back to haunt you.
Here's another example, a little easier to calculate. We buy a lot of blueberries - it's one of our favorites around here. The clamshell packaging looks the same, and it's the same surface area. The difference is in the weight and depth. (and price of course)
And finally, this one is really interesting. Which one is it - 375 or 500 grams?
I wasn't trying to turn this entry into a trip to the grocery store, but more a marketing awareness opportunity. To maintain a good reputation and build a loyal customer base it's important to be consistent with your current market. If you try to deceive or take advantage of customers, you may get away with it once or twice, but eventually people will recognize what you've done and we all know how difficult it is to regain the trust of a "lost" customer. This principle will apply just about anywhere, not just at the grocery store.