1) fake review/counterfeit problem 2) support mom and pop
Google Shopping is trying to go after the "amazon prime for the rest of the internet", which seems like a good idea.
On 2), One thing to do would be to do what doordash did, just go to 50 mom and pop retail stores in one region and talk to them. see what their problems actually are.
The fake review/counterfeit goods problem is actually pretty hard to solve, but it's interesting because it's not on amazon's top 3 problems list, so you could disintermediate. Ways to solve it that may be businesses: machine learning, limiting manufacture geo's, relying on video product reviews with trusted influencers, tracking PE acquisitions as a proxy for brand deterioration, reading negative reviews first, etc.