A pre-purchase inspection is often carried out when an aircraft changes owner. The company carrying out this kind of inspection is placed "between" seller and buyer, so to speak, and ensures that all major items and components are checked and inspected. After that an agreement between seller and buyer is made that sorts out what jobs need to be carried out and who will bear the costs for the agreed, final repair. As a result, pre-purchase inspections are very much a question of mutual trust to the company in charge.
See photos here