Beware of counterfeits when buying razor blades on Ebay. Copies of both the Mach 3 and Fusion razor blades are being sold.  The copies may look authentic if not studied carefully and are often sealed in a factory packaging. The quality is poor, however, and I would not recommend using them. One way to distinguish the fakes from the real ones is that the fakes do not have real lubrication/indicator strips, it's just paint/plastic. Furthermore, the fake cartridge holders do not have a serial number on them.

Buying from a seller with good feedback is not a guarantee for receiving authentic blades. I received fakes when buying from a seller with 100% positive feedback (johnfrase). Unfortunately, I did not notice they were fake until after I had given positive feedback. The mentioned seller still has 100% positive feedback, even I know several others also have received fake blades from the same seller. In fact, it seems a lot of buyers do not leave negative feedback when receiving counterfeits, in fear of receving retaliatory feedback themselves.