When I purchase non genuine parts I expect the seller to be selling parts that meet a certain standard. Now it is fair to accept that a non genuine part might not last as long as an OE part, but they should still perform and last a reasonable time. Occasionally you will get a faulty part and this can also happen with OE.
I purchased a water pump from Repco last year for SWMBO's fairlane. It started to leak after 5,000 km. I could not find the receipt so had to cop it. I got another Repco branded pump. It comes with a two year warranty so it must be reasonable quality.
A couple of years ago I pulled apart a falcon water pump to use the bearing for my TDI fan. It was a non genuine pump and the bearing was a smaller diameter the genuine pump bearing.

