Fairness means that the data controller or processor should only handle personal data in a reasonably expected way. Fairness principle means questioning, not only if you can use the data, but rather should you. Processing of personal data must always be fair and lawful.
In your fairness assessment, you should ask how you obtain data and if someone is misled or deceived when the data was collected. Ask how your processing affects one individual person and affected individuals in general.
