Yea I think I remember Baki telling them that the Leader of Wind cut their military power in half and started giving high paying mission's that should have went to them to Leaf. In fear of Sand being completely destroyed they decided to raise the level of ninja with Gaara being the test subject. So I'm guessing the assasins were low level ninja's that they could no longer afford to pay and that prob had no chance of defeating Gaara like his Aunt. So in the end I'm going with your Gaara had misplaced hatrid answer.