To cheat a native English speaker...

[Tdol]

I agree with you, ILKB.

[Philly]

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I agree with tdol's first post. There are very few non-native speakers who I mistake for native speakers, but there have been a few.
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I think it's important to mention, though, that I've been teaching English for almost 20 years, so it's much more likely that someone like me would recognize that someone isn't a native speaker. "Regular" native speakers don't notice all the things that I notice.
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[sastewart930]

The only time i've ever NOT known was when I met a guy from
Denmark. He could have told me he was from Minnesota
and I would have believed him.

[riverkid]

Originally Posted by nyggus

Do you, native speakers, always recognize that a text you're reading is written by a nonative speaker?

In this case, Nyggus, the use of 'cheat' was a dead giveaway. ENLs would use 'deceive, fool, trick' or maybe some other word but not 'cheat'.