OP. It's not a good idea to try and do this unless you very confident in what you are doing and ALSO are clear with the guy that is going to purchase it so they know the implications.
If you sell your iPad with just your personal details removed the new owner will NOT be able to effectively sync the device with their computer and iTunes because the partnership exists with yours. I doubt that is what they will be expecting when purchasing the device. They will need to restore and then will lose their jailbreak unless you have saved SHSH Blobs on Cydia, but I'm guessing that if you had those you would restore anyway. If you are commanding a premium for the device being jailbroken you are essentially selling them a pup, unless they fully understand the ramifications.