There's an entire black market around creating forgeries of branded SFPs and other transceivers. Source, I've been bitten by it. You may think you're buying a

There's an entire black market around creating forgeries of branded SFPs and other transceivers. Source, I've been bitten by it. You may think you're buying a branded SFP from a vendor(Cisco, Juniper, etc), when in fact the vendor in question has not tested that SFP with their gear. There are subtle differences in SFPs and there is good reason to have them tested with your vendor's gear. Not saying the price hike for vendor certified optics is justified, but link flaps cost time and money.