I suspect they go for FSA because it's at the light end of the mass market (or was until Enve showed up), and has bonkers RRP that's often discounted anyway. If Merlin are selling a £500 chainset for £150, then the £100 one on ebay must/might be legit?
Got me a little worried after purchasing a FSA Orbit MX headset from Absolute Cycles for £16.95 recently. Its only a little cheaper than PX and others so hoping its alright. I can't imagine headsets are where the money is for fake good unless say it is Chris King.
I've had a fake Cane Creek S8 before, it wasn't even that cheap or from a particularly dodgy looking shop. Rusted and siezed in a matter of weeks. The original has sealed stainless bearings isnide a cup with a big thick seal on it and lasts years, the fake was just a generic sealed bearing headset.