In this video, a Canon print cartridge is opened up and revealed not to contain the meagre 11.9 ml (0.4 fl oz) of ink it is advertised. The proposed solution is to buy a printer designed to be manually refilled with bottles of ink (such as the featured Epson EcoTank ET-2850), though it has only been tested briefly.
I’ve always ordered ink from inkjets.com because it’s cheap and their cartridges are completely clear so you can actually see that they’re full of ink like you’d expect.