- If you have not opened the package, you may mark it "Return to Sender," and the Postal Service will return it with no additional postage charged to you.
- If you open the package and don't like what you find, you may throw it away.
- If you open the package and like what you find, you may keep it for free. In this instance, "finders-keepers" applies unconditionally.
from Receipt of Unsolicited Merchandise (USPS)