When a native #Chinese speaker praises you for your #Mandarin and you're a foreigner, it means you suck.
When a native Chinese speaker says that your Mandarin sucks and you're a foreigner, that means you're nearly proficient but you need to be better.
But if you're Chinese learning to speak Mandarin, unless you speak with a flawless accent, quote chengyu in your sleep and read the classics, you suck. And even if you do all three you will still suck cos there's always room for improvement.