Fully decentralized marketplace? Seizure resistance? How? How can it be a seizure resistance if its so decentralized that there is no moderation and people will be able to submit illegal things? By giving absolute freedom, it will turn into a darknet and not a normal marketplace.
In its purest form, with absolute freedom, it would indeed allow anyone to sell anything without restrictions. If the wrong community gets to know it, it would indeed turn into an unstoppable darkmarket. That's why a governance system is mandatory. One could get a product / seller banned by voting. Enough votes lead to listing erasing. After a first report, the product wouldn't be accessible to anyone until vote ends.
Illegal products wouldn't remain accessible more than a couple hours.
I also pictured some members roles, where most trustable users ( dispute ratio, number of orders ... ) would have more weight in votes, and would moderate the market. They could get a revenue from a dedicated pool even.