Professional skepticism
In one sentenceAn attitude of mind that makes the auditor question and assess evidence carefully, and not accept management's word or a weak document as established fact.
Simply put
Professional skepticism does not mean accusing management of lying, nor believing it without evidence. The auditor stays alert to any contradictory document or unconvincing explanation.
It matters even more for items that depend on management's estimates, such as provisions and impairment.
Example
The sales manager said the rise in receivables in the last month was due to a large new customer, so the auditor asked for the contract and a confirmation from the customer itself, rather than settling for the verbal explanation.
Don't confuse it with
Auditor independenceIndependence is a condition of the auditor's relationship with the business, while professional skepticism is his way of thinking during the examination.