I'm always amused to hear someone "tanked" their interview to put clubs off. Interviews and psychological tests at the combine are designed specifically to reveal things the candidate wants to conceal. Do you honestly think an eighteen year old schoolboy can fool a raft of experienced adults who have heard it all over decades?
Honestly, if a draft combine candidate can "fool" you, you don't belong there. I've never seen, nor experienced, someone pull the wool over recruiters when it comes to the character and personality testing disciplines. Don't forget, these kids have been watched for years. Their characters are dissected, along with those of their families and teachers or employers. By the time they get to the interview, they have been independently tested as well.
The interview is merely a fait accompli. It is a chance to clarify discrepancies and to delve into areas that have not been covered off as thoroughly as others.