Scenario 1: Daniel offers to give Adam a chocolate bar if Adam gives him £1. Adam accepts.
Scenario 2: Frankie promises to give Kieran her old laptop at the end of the month, without asking for anything in return.
Scenario 3: Olivia buys a 12-month mobile phone contract. She will pay the phone company £20 a month, and in exchange, she gets unlimited texts, calls, and data usage.