Well when I cross-posted this on hongkongcard another member of some standing there came forward to say he's been subject of a similar closure
http://forum.hongkongcard.com/forumS.../18044?page=11 #107
He admitted to one sale.
But otherwise his account is relatively orderly: 5-6 years membership, have only three people on his redemption list, never paid to refresh or change his redemption list.
Latest discussion on hongkongcard is drawing attention to the identity of the buyer - he may be a habitual buyer of many members' awards and so caused all his sellers to be flagged. The hongkongcard member admitted this may be a possibility.