I have long believed there are cheap copies out there and that they have inferior internals, I'm not sure you can spot them until they are stripped, counterfeiters are very good at what they do, Darren Dawes has had his Dawes Valves copied and you wouldn't know until they are pulled apart and you see the machining on the inside.
I do not buy fuel pumps and many other significant components unless they come from a well known reliable source, I have just bought a Carter Black 4601, I bought it from the States from a place I know trust.