In retail (or any market with elastic pricing, not sure if I'm using that term correctly), collusion is really hard to gain hard evidence (evidence that will hold up in court) using data alone. You need to use the data as a tool for on-the-ground and in-depth qualitative analysis. I would not be surprised if this holds "even more true" for consumer goods like this than it does for other, highly regulated fields like finance and healthcare. I personally like the idea of focusing on an individual good or category of item, and seeing if you can find similar patterns, in other goods.