I have been dealing with Takeshi only on home carts for the last 12 months until Shinichirou started accepting credit cards.
3 key advantages Takeshi has over Shinichirou:
1. Selection: Takeshi sells not only Neo-Geo, but also PC-Engine, Super/Famicom, and pretty much anything he can find in Japan. He lives in Akihabara, but he hunts for games from stores throughout Japan, some of the games he found for me are from Hokkaido.
2. Communication: Takeshi used to live in US, so his English skills are like ours, even better than some of us in US.
3. Unlike Shinichirou who only responds during sales inquiry, he'll email you when he receives the payment and when he ships out the games.
Price is not always an advantage since some games are higher than Supersellers but the other way sometimes, so I call that a draw.
One thing to remember now, Takeshi has a full time job now and he only does game hunting during the weekend, so if you don't receive the reply, just be patient. The best time to contact him will be Fri evening (here, Sat morning in Japan) for inquiry so you can finalize the deal over the weekend and confirm what you want by Sunday night.