Selling on that website?
Seems it's not just a website. They built an app called also DEM Market. According to virustotal the app is safe but i think someone experienced enough has to tell more about this app.
OP didn't tell anything about the app or the smart-contract which also need to be vrified before inviting people to use it. The idea seems to be original but how to convaince users that they can exchange illegal stuff in the internet in a secure way? Users choose Tor as the best trusted tool for anonymity, so why they have to choose your market.
About the website, there is litterally nothing except some few available trades.
Yea you are right, the point is "to convaince users that they can exchange illegal stuff in the internet in a secure way" or it is a bit hard to change their habit in using TOR. Or most users can now still accept the DDoS drawbacks (accessing the web in very bad conditions) or they don't mind to try to find out live mirrors, versus taking risk in trying a new approach which are not sure if leaking their identities.
When one day the attackers are more strong, Tor will suffer from the drawback of IP masking, which is its inborn deficiency.