How does Amazon sell a 300.00 cartridge for 180.00?

Millercarbon nailed it and Amazon right on the head.  Bravo!
Although this conversation really had very little to do with cartridges, erik, why did you qualify your remark by the preface, "in the old days"?

Bill, there is no such thing as grey market, the market is always black. And you know it better than I do - New York, New York..
That piece of junk cartridge costs $5 at most, Amazon Japan price is very high.

For the first time I am agreeing with millercarbon. Go figure.

inna

... there is no such thing as grey market, the market is always black ...

This is simply mistaken. Black market merchandise is illegal, by definition. "Grey market" is merchandise outside of officially designated distribution channels. It's perfectly legal, even if it's dubious ethically.

in the old days cartridges were among the highest markup items around, about 10x their cost. Kind of like tooth brushes at the pharmacy. Insane markups.

More true for audio cables than for cartridges.