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1 - Low end PC
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2 - Network problems.
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The check is already more advanced than that - it checks your fps every server tick (5-10 times a second, not sure exactly), and adds an value that increases depending how far below the fps threshold it is. If you still get tagged for low fps, it means that it happens consistently enough to potentially give you some advantage.
Also, I recently tried out samp with just intel HD graphics 4600, and I never got the warning, even though that video card is in no way enough for any kind of normal gaming, so if your computer still can't run it, it's probably time to do something about it.
As for network troubles, that sucks, but unstable network is generally very hard and annoying to deal with for everyone involved either way and we can't really do anything about it. We might adjust the thresholds a little bit, but don't hold your breath.