Ending things with 9, 99, or having "discounts".
E.g. $50 is ugly, so bump to $49, and now that people know of that trick
(due to learning the marketer), it’s now $48 Because human brains look
for the first digit. Alternatively, humans can compare princes
frequently to find the better deal, so if one is $8 and three is $20,
even when $20/3 is clearly a terrible price, there is an urge to
buy.
It's an example of the G.I. Joe Fallacy: You know it's there but
it still tricks people, so it's used!