Liquid gold - Ever considered to invest in printer ink?

My fax machine, a T-Fax 361, needs a new ink cartridge. Why does it need a new ink cartridge? Well, because the old one is empty. Why is the old one empty? You guessed it, after receiving lot's of fax spam, when forgetting to unplug the device again after using it.
Thanks, German Telekom for making the registration of fax devices/fax numbers mandatory a thing a few years back! Who could have known, that public records could ever be abused.

Ok, off to the local hardware store, just to find out, that a brand new BX-3 cartridge would cost more than 30 €. However, a refill can be had for a "mere" 18 €, so a refill it was (with some gnashing of teeth).

I seriously begin to doubt the business model of fax advertising here. The junk, these people send usually almost turns the pages from black on white to white on black, costing a fortune in terms of ink. They must be aware, that everyone hates them and it's completely beyond me, why any fax owner would actually buy something, offered this way (except of course, if it is a baseball bat engraved with the home address of the marketeer).

I have two theories about the whole issue:

1. OEM's use distilled tears from clubbed baby seals as the liquid component in printer ink, while refillers merely use imported table water from Japan. The black pigment is probably taken from the souls of those telephone company managers, who make money from special deals with people, sending such trash.
2. Fax spammers don't really try to sell any products. Instead, they must be employed by ink suppliers to make sure, people still buy consumables for an otherwise outdated technology.