How to Identify Genuine HP Cartridges?

I recently bought an HP Cartridge for LaserJet printer 3600 series, it’s only four months since then but the ink is almost over with the printer reminding me to replace them, this my first time purchase, I have been using the cartridge it came with and taken about 4 years, I contacted the retailer only to tell me that his hands are tied. Is there a way to identify whether these are refilled cartridges?
