Interesting question! I've checked with our legal team, and based on what you've described, I do not believe Square would be the right payments platform for you as your marketplace may violate our terms of service.
Here's how it breaks down:
Our terms of service states the following: "By creating a Square Account, you also confirm that you will not accept payments in connection with the following businesses or business activities: (1) any illegal activity or goods..." Currently, marijuana is still illegal under federal law, and federal and state laws are part of what we used to define "illegal activity or goods."
