Retro video game cartridges are collectibles and some of them can be very valuable.
Make as huge a profit you can make from the unsuspecting fool who is rich enough to pay you a small fortune. Retro/old game consoles and game cartridges have sold for thousands of dollars on EBay.

Don't think I can help you there, since I couldn't bear myself to sell my old videogames. Heck, I've got most of them still tucked away at my parents house.

I've got a few games myself that garner quite a high price on the market, such as the PAL version of Panzer Dragoon Saga and Dragon Force (heck most PAL versions of Saturn games are expensive), though I won't ever sell them myself.

If you acquired it fairly for $2 and didn't rape or murder anyone in the process, then I don't see anything wrong with selling it for $70...

Theres nothing immoral about selling something at market value

Does Amazon US ship to Japan?

I do it all the time as a hobby.

I buy and sell SNES games on eBay. I have two strategies. One is to buy SNES collections and split it up (after fixing/cleaning it) and the other is to buy games from regions where they are common and advertise them in regions where they aren't.

For example, the German and UK Hagane cartridges are identical (as a quite a few European games are), but the game sold much better in Germany. Hagane is now wanted by UK collectors. I can import a copy of Hagane that's listed on eBay in Germany for £25 and sell it to a collector in the UK for £50. The only downside is that the amount of buyers is limited. I often wait weeks, sometimes months, for one game to sell; this also means the market is easy to saturate too (there isn't room for two people selling the same rare game like this).

But do I feel bad about potentially making 100% profit? Not at all. I feel as though I've earned that profit by providing a service.

The way I look at it is that my customers are willing to pay a higher price in order to save the time and effort of looking for rare, good value games from other countries. Really, what they're paying for is the convenience of not having to do all the ground work themselves, because I do that for them. It's the same with you too.

Market is always right.

As much as the market forces allow.

Only books, CDs and DVDs. Nothing else. :/

Thanks for all the opinions.
Makes me feel a lot better. :)