I definetely don't trust any exchanger service, because mostly their not give a private key. What an exchanger which can give you a private key?
exchanges will probably never give us a private key as our deposited coins directly get sent to several wallets in a mixing process and eventually end up in their cold or hot wallets.
That's how the exchanges work, our bitcoin goes to their wallet
And in their web app we "play" with numbers to exchange coins from one to other.
Then when we make the withdrawal request the bitcoin comes from their hot wallet, there is no room to trust your money in exchanges.