Shorting Stocks CFD, incur little or no overnight holding cost ?

Recently, I try demo accounts in many CFD Stock Broker in UK and Europe.. I found that some broker charge little or none for holding short stock cfd position overnight.. While in the real US stock exchange u need to pay interest from 5%-20% for holding short position.. How can CFD broker provide this kind of too-good-to-be-true trade ? Where they route the trade ? What exchange ? Who take the other trade ? Supposedly if a client is a good value investor, or hedge funds, he can become very profit