Customer service. Scenario 6 of 6. Owning a mistake
You gave the wrong price
You work in a phone shop. Ten minutes ago you told a customer that a contract was £25 a month, and she went to fetch her ID. While she is gone you realise you read the wrong line. It is £35.
She comes back smiling, ready to sign.
The principle
When you have told a customer something wrong, correct it before they act on it. Say what you got wrong, apologise once, and offer what you can do now.