Cartridge without serial?

Manufacturer sell cartridges only to his distributors in every region (Asia, Europe, America ...).

Distributor have to buy large amount of carts to get special wholesale prices.

Distributor can sell to the dealers, small shops or to private individuals online, but ONLY in his region!

I think the broken link is Asia and some distributor (or dealer) who can’t sell so much and willing to get rid of many cartridges quickly for very low price. This is a violation of the ethics, there are recommended retail price for dealers, when someone illegally sell for lower price worldwide on grey market (ebay) other dealers suffer.

When serial number replaced with fake number it’s impossible to track down the rat.

This is how it works in my opinion, maybe it’s more complicated, but manufacturer is happy to support only honest distributors, they are very important for manufacturer who can’t sell direct to the buyers.

It's not the consumers fault - consumers will buy at lowest price if all things equal.  Sounds like the mfr isn't willing to do much at the top end and wants to blame the consumer.  I think the mfr's should own up to their product and provide support regardless where it was bought.  There are some companies that do that. Recently, I was talking to Tri of Tri-Planar who said that he supports his products regardless of where it was bought. Now that's ethical.

@chakster  You explanation would apply for a very large conglomerate that sells very high volume.  I highly doubt that any of the cartridge manufacturer's are in that league. Surely they must know all of their distributor's and exactly what product they are shipping to them. I would be surprised if Nakatsuka-San is making and selling a hundred pieces a year-- in total! 
Therefore, it seems odd to me that this situation is going on, unless of course something else is occurring ( which I suspect strongly that it is!).

cartridge without a serial number would make me wonder if its real, knockoff/or stolen.   

@daveyf even if you know your distributors how you can catch one who sold to grey market dealers a bunch of them (if serial numbers replaced with fake number)? This is the only reason to remove or to replace serials, this is ID of the source.