Does agricultural certification (like Fairtrade) reduce poverty? Dr Carlos Oya

I buy Fairtrade bananas, assuming farmers are getting a better deal. But a new systematic review finds that agricultural certification only results in a marginally higher price for producers, does not improve household incomes, and negatively affects farm workers' wages. Why is this? And how should we respond? You can read the World Development paper here, by CarlosOya, Florian Schaefer, & DafniSkalidou https://www.sciencedirect.com/science/article/abs/pii/S0305750X18303012 Ungated summary: http://www.3ieimpact.org/media/filer_public/2017/06/07/srs9-agricuture-certification-scehmes.pdf