They will check directly with CRA. The things they will need to verify is weather you have filled your taxes and weather you have paid something if you have to pay back to CRA.
If you didn't work that means that there is nothing to pay back but you still have to file your taxes.
They will refund a portion... My wife had to withdraw her application because of a calculation mistake. They did not sent any document back, but we did get a refund.
FYI: For my wife, she received RQ, and as we were filling the form, we realized the mistake and simply withdraw the application and submitted a new one. CIC did NOT RQ my wife the second time and she got her citizenship in 15 months.