1. Violation of terms, red-flagged accounts, suspicious activity, hitting the alarm, etc.

2. Read and follow Terms of Service. Make a habit too of reading the FAQ section.

3. Since you have mentioned, at least with no KYC, Binance should be your best choice. KYC is not necessary for Standard Accounts. However, to increase your account limit, you need to comply to their KYC.

As for the case you have shared, HitBTC exchange don't have a good approval rating here in the community. There are reports of closing and freezing accounts without a clear reason. We don't know the reason why your friend's account got frozen there but for a safe side, stay away on that exchange.