From a US News & World Report story called “10 Ways Consumers Are Often Duped” …

There are a few tricks that retailers use to get us to buy their products, including these:

1.  They put things in tall, skinny packages.  In most cases, they could fit the same product in a short, wide package.  But studies have found that when we see a tall, narrow box, we automatically think there’s more in it.

2.  They CLAIM something’s cheap, and we believe it.  In a 2007 study, researchers offered overnight shipping for “a $5 fee.”  Then they changed the ad so it said “a SMALL $5 fee” . . . and suddenly 20% more people were interested.

3.  Rebates.  Most people think they are getting a better sale price, but often never send in the rebate.  Usually, the posted price is the AFTER rebate price.

4. “Buy 5 for $10” or some variation of that deal.  You can usually purchase just one for $2 (the same price), but people are more likely to buy the 5 items.

Read more here: US News and World Report