At this time I think about few ways:
1. Implemented. The classical verification by seller company, address, etc. For customers it looks like simple Verified label in the Product card.
2. Payment cancellation system and money refunding. In my opinion, this is a good suggestion for the customers but isn't for a sellers.
3. The 'Penalty Fund' - it's a new idea specially for the cryptocurrency services. For example, when purchased product has a low quality, customer have opportunity to cancel the payment, but funds will be transferred to the Project Fund. This variant makes 0% seller commission to forever and motivates to upload only hight-quality content. This idea need a focus on testing before jumping.
What is better in your opinion?