Testing op amps

I bought a bunch of op amps on ebay and I am doubt they are fake. How can I tell?

For instance, I try to null offset a TL071 and it always show at least 300mV at the output (+/- 16 V supply, both inputs at 0 V) as shown on the data sheet, with a 100K pot and a 1.5K resistor connected to Vcc-.

Is it the amp is defective or I do it wrong?
 
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