Day 87: Do Sanctions work?

On September 19th, U.S. President Barak Obama decided not to impose sanctions against Malaysia and Thailand for failing to meet minimum standards in combating human trafficking. For two countries that were downgraded in the State Department's annual assessment this past June, why is the a lack of pressure on Malaysia and Thailand to change their standards?  If the U.S. were to impose sanctions, do you think they would work?