I don't think they really clone IC's, they either sell empty packages or relabel/repackage existing devices, for example sell an LM358 as AD8620. I have heard of fraud with FPGAs, so I wouldn't rule out MCUs. As a general rule, I would be more worried about an expensive AD8620 than a jellybean uA741. But I have received carbon film resistors sold and marked as metal film, and this would save them much less than a cent each. The best defense in my opinion is buy from reputable sellers, since it's hard to tell if you got a rejected batch.