"If you decide to downsize your product, you should reduce the size of all three dimensions — height, width, and length — by an equal amount. Consumers are less likely to notice a change in all three dimensions."
"People will perceive your price to be smaller if you display that price in a smaller font."
"People will perceive your price to be lower if it contains fewer syllables."
When I shop, I look at the quantity. If my chocolate has 90 grams instead of 100, I'll immediately put it back and look for another brand - because it's too hard for me to compute how much I would get swindled of.
I'm not sure whether it's a practice everywhere, but many shops in NYC also indicate the "per unit" price: per gallon/oz/pieces etc. I use it all the time, and I wish it was mandatory by law for all products.
I live in Spain and when you go to supermarkets, all price tags on the shelves and on supermarket-packaged products (pre-cut meat, for example) indicate the cost of the product per unit (big numbers), and per kilo (small numbers), so, if you want, you can quickly and easily compare a package of, say, 136g of meat with other packages, without weight interfering. You can see easily the price per kilo of each kind of meat.
"If you decide to downsize your product, you should reduce the size of all three dimensions — height, width, and length — by an equal amount. Consumers are less likely to notice a change in all three dimensions."
"People will perceive your price to be smaller if you display that price in a smaller font."
"People will perceive your price to be lower if it contains fewer syllables."