Do you think this is a scam? Have you ever been scammed online?

very common scam, report it to Craigslist so they can remove the post and call your local police. Cut off communication with this person, do not send any money, unfortunatley if you sent money thru Western Union or Moneygram your 250 is gone forever and no way to ever get it back. There is no such thing as an anti-terrorist certificate to clear packages in Nigeria