Well, interesting question and not sure that I can add much but just want to join the thread to see the responses -
If you registered your iPad, then Apple should only know the information that concerns you, so unless the 'potential buyer' has broken into Apple's servers, I doubt that you are at risk; of course, I'm assuming that you will reset the iPad back to 'factory settings' when sold - the serial number will still be available (it's like a SSN).
NOW, this is an interesting
SITE - by entering the last 3 or 4 characters of the serial number, the 'basic' information of the iPad will appear (for myself I enter the last 4 characters which returned the basics) - you might want to just provide that information?
Will await further replies and please post back your progress in this sale - Dave