While trade sustainability impact assessments (trade SIAs) have generated much useful information about the potential impacts of trade liberalisation, they have made very limited impact on trade negotiations, which generate unresolved controversy, if not deadlock. This paper contends that one reason for this is that trade SIAs do not explicitly recognise the motives for countries to resist free trade. Five such motives are identified, with very different characteristics and validity from the perspective of social welfare enhancement and sustainable development. The paper suggests revisions to the trade SIA methodology to help decision-makers better understand the obstacles to trade liberalisation negotiations and whether it is likely that these obstacles will, and desirable that they should, be overcome.