Marshall - 4:19 pm on Oct 21, 2012 (gmt 0)
That applies to unsolicited receipt of merchandise, not a mistake trying to fulfill an order.
Also from FTC site:
Q. What should I do if the unordered merchandise I received was the result of an honest shipping error?
A. Write the seller and offer to return the merchandise, provided the seller pays for postage and handling. Give the seller a specific and reasonable amount of time (say 30 days) to pick up the merchandise or arrange to have it returned at no expense to you. Tell the seller that you reserve the right to keep the merchandise or dispose of it after the specified time has passed.
Bottom line, you screwed up and the receiver is under no obligation to return it. It is one of the costs of doing business. Learn from it and move on.