From inkjet cartridges to permanent markers, you'll surely find a refill, licensed and unlicensed, for it. In this particular post, however, I'll focus on inkjet cartridges.
I, for one, find it impractical to buy a new ink cartridge every time my printer runs out of ink because of the pricey price tag that comes with new cartridges. It is acceptable since in nations like where I am living in right now, the Philippines, brand new cartridges are waaaaay expensive. Thus, I am forced to have my cartridges refilled instead. I said 'forced' since if I have the choice (and enough money), I'd rather buy a new cartridge because some say that refilling an ink cartridge might cause the printer to malfunction.
Having inkjet cartridges refilled is not cheap, too. Perhaps, for people living in North America or Europe, paying $6 just to refill your printer ink is REALLY cheap, but in most Asian nations, $6 is still a large sum. Why, you could already buy 2 dozens of donuts with that amount here already!
One remedy that many people use aside from refilling (if they are worried about their printer malfunctioning) is to use generic refills or refills that are not of the same brand as their printer's. Generic refills are as safe and as reliable as the branded ones, but not as expensive. The only drawback, however, is that this is not covered by the warranty of your printer, so it's better to use an original cartridge. But, then again, malfunctions triggered by refills are not covered as well, so what should you do now?
In the end, you'll have to buy a new licensed cartridge for your printer. But if you really can't afford it right now, you can always take the risk.