Top 5 exchanges for shorting and margin calls

Huobi Pro- Verification required, numerous pairs to short, easy registration, low fees

Available at: https://www.huobi.br.com/en-us/topic/invited/?invite_code=rzth3

Poloniex- US based, verification required, leverage -2.5, only a few pairs to short

Available at: https://poloniex.com/marginTrading#btc_eth

Bitfinex- verification required, minimum of $10 000 USD
Available at: https://www.bitfinex.com/

Kraken- verification required

Available at: https://www.kraken.com/en-us

GDAX- verification required

Available at: https://www.gdax.com/