How we change what others think, feel, believe and do
Preferred Number Pricing
Use numbers in your prices that people like. If in doubt, use seven, as it is by far the most popular number.
Combine this with other effects, such as First Digit Anchoring.
A shop prices items at $19.97 rather than $19.99.
A retailer increases an item from $6 to $7 and ends up selling far more.
Rather than pricing at $4, a retailer plays on the 'zero' effect that makes a thing seem free by using $04.00.
People choose things that make them feel good, for whatever reason. Even though they may not consciously know that a price contains a liked number, they will still be influenced by any sensory factor, including number.
A global survey of 30,000 people by Alex Bellos resulted in the following top ten preferred numbers: 7, 3, 8, 4, 5, 13, 9, 6, 2, 11.
Numbers can be related to culture, for example eight is popular with regard to the 'eight ball' in pool. This also highlights how you can find a good reason for pretty much any number. Two has symmetry. Three forms a triangle. Four a square, and so on. Zero can also be a good number to use as it may be associated with 'free'. Other associations can also be used, for example '100' meaning 'everything' or 'perfect'.
Another way could be to use the values set by money notes, such as $5, $10, $20 and so on. This also makes it easier to pay cash for something.
Bellos, A. (2015). The Grapes of Math. Simon and Schuster [published as 'Alex Through The Looking Glass' in the UK]