By reputable I meant that 2juki has excellent customer service, as mentioned, and will make thing right with no fuss if the product received is not as described. I can vouch for that myself, as can many of my friends and it'll only take a minute or two of googling to confirm it on a plethora of audio forums.
I can confirm myself that serial number on my $3500 Zyx Airy III was fake, this number does not exist (i have checked with manufacturer), the manual was blank without any serial number at all. You never know what you're buying and the seller change serial numbers. This is a bad sign, also none of the manufacturer will help him or a buyer with any issue, never.
In 30+ years I've only once made use of a cartridge manufacturer's factory retip service, something I will likely never do again. Hence I'm more than fine with grey imports (be it cartridges or most other things) and with putting the considerable amount of money saved towards other things or letting it remain in the bank.
If it's a cartridge then you can only retip of refurbish it by someone else, but the manufacturers actually change the old cartridge to a new one for their customers (special price), and this is what you can't do with grey market cartridge.
I will never buy a grey market cartridge after my own experience with juki and Zyx.
I can not speak about all cartridges he's selling, but some cartridges are special and it's not a good idea to let someone else work on it (recantilever or retip it) as it will affect the sound signature.
I can undestand why some people are buying grey market cartridges, the only reason is to save money. In my opinion it is better to buy a demo unit from official distributor or used sample from another audiophile, those carts are under warranty and can be upgraded by the manufacturer easily. Also some of the distributors can offer a nice discount even on brand new cartridges, some of them are aware of juki and his grey market stuff, but they can do much more than a chinese grey market dealer, at least they can speak english to discuss any issue.