Just google use your key words "Buy the rumours, sell the facts" and found this :
http://answers.yahoo.com/question/index?qid=20080902230659AAhluqi
Part of what it says is :
In real life, a conservative person would buy on facts, and sell on facts. Would you prefer to marry someone because there was a rumor they would be a good partner, or because you knew they would be a good partner? :)