Hi Lauda, why you think they are a shady exchange?

Every now and then a scam accusation pops up, and there are ones unresolved that are several months old. Use your brain.

I have heard about unresolved support message for dead coins, but not big and "real" scam accusation. Can you explain please more?

The magnitude is completely irrelevant. If you scam $50, you're a scammer. This exchange is highly shady and you should stay away from it.