The core idea here is if the user adds a given trait to a list as "willing to give/take", the user should be able to then add the same trait to another list as "willing to take/give" (dependent on the earlier choice).
Obviously, if the user adds a trait with "willing to give and take", the user should not be able to re-add the same trait to another list, as 'both situations' are covered, so to speak.
This would allow users who find taking a particular interest to be core to their experience but aren't so sure on giving the same interest (or vice versa) to express this 'correctly', rather than making compromises.
(Of course, depending on the current implementation of interests, this might be non-trivial.)