These are used OEM cartridges that have been cleaned, refilled, and tested for quality. Thus, they look the same as OEM cartridges but are way cheaper.
However, take note that there are also downsides to third-party cartridges. They won’t always work smoothly with your printer, especially if you buy from an unreliable supplier, and can clog your printhead and leave visible bands or streaks in your documents.
So if you decide to buy aftermarket cartridges, make sure that they come with satisfaction guarantees, warranties, and refunds. It is also crucial that you carefully choose an aftermarket cartridge manufacturer.