Interesting thread. I have a tray of various cheap chinese opamps, and so far as I can tell none of them are fakes, at least parametrically. The 324's go down to ground and up to about Vcc-2V, with typical 324 output quirks (can only sink a tiny current, and need a 10k pulldown resistor to get down to 0V output when sourcing current, etc) and crossover blips, GBW and slew appear to be on the money, input offset are within norms, etc. Same for the 358's, TL072's, MCP6002's, etc. Maybe I lucked out? Some are obviously re-claimed silicon, but, all that I've tested appear to function to datasheet specs.
How were you able to ensure you were going to get fakes? What are the warning signs? Price? (I think I paid $1 for 50 SOT LM358's, that seem to perform as expected)