Terms of Agreement for the APP: said:9. Transfer of Plan
You may transfer this Plan to a new owner of the Covered Equipment by sending notice of transfer to AppleCare Administration, P.O. Box 149125, Austin,TX 78714-9125, United States of America.You must provide the Plan Agreement Number, the serial numbers of the Covered Equipment being transferred, proof of purchase of the Plan, and the name, address, telephone number and email address of the new owner.
blackmagicxx said:pitfalls of buying used would be the same as buying anything used, Never know where it has been or what has been done to it.
If you know/trust the seller then there should be no problems, just check it out first.