It can be insanely hard to find any demand for them if you’re talking about trading locally rather than selling online and shipping. That’s probably the biggest real obstacle.

In terms of legal or regulatory issues, no, nothing is stopping you unless maybe you’re dealing in porn-focused games in a state with strict anti-obscenity laws. Don’t lay the 18+ doujin soft out on the Sunday flea market table in front of your local superior court.

Just in case: So-net is Sony’s ISP in Japan. If you haven’t lived there and used their services, this doesn’t affect you.

Not saying Sony doesn’t have a lot they need to fix or anything, just don’t freak out unnecessarily. End PSA.