They don't need to get you to admit anything. They have a log right in the ECU telling them when you over-reved the car and by how much. By over-reving I don't mean over the red line.
The following article defines the over-rev stages for an older Boxster (987) which has a different red line, but you get the idea.
Engine over Revs
Understanding Porsche rev range activity. A detailed guide from Porsche specialist dealer 911virgin based in Uxbridge, West London

You can ask for a Pre Purchase Inspection report about over-revs record, if you know this a-priori. You can see how many times WOT was used in the first 10 hrs of your car of choice.