Thursday is the main market day in Jimma, when farmers and traders from across the surrounding highlands converge on the city. The market is large and genuinely commercial rather than tourist-oriented — you are as likely to be looking at sacks of grain and live chickens as at craft stalls, which is part of what makes it interesting.
Coffee is the thing to pay attention to. Jimma sits at the centre of one of Ethiopia's major coffee-growing zones, and the range of beans, grades, and processing styles on offer is wider here than in most Ethiopian cities. Local roasters sell coffee already processed and ready to take home. Spices — cardamom, ginger, berbere mixes — are also good value. Handwoven baskets made in traditional Oromo patterns are the most practical craft purchase. The market is at its liveliest in the morning hours before the midday heat; arriving by 8am gives you the best experience.