I worked out what i was doing wrong
SELECT
DISTINCT MATCH(title, description)
AGAINST ('search string' IN BOOLEAN MODE)
AS relevance,
d.id, d.title, d.description, m.image
FROM deals d
JOIN merchants m
ON m.id = d.merchant
WHERE d.status=1
AND MATCH(d.title, d.description)
AGAINST ('search string' IN BOOLEAN MODE)
ORDER BY relevance DESC
LIMIT 0,24