[clayrichardson]

Getting liquidity to short or long on margin is as easy as clicking a button and getting liquidated.

Poloniex, Bitfinex and BitMex are some of the places you can play that game. You can even become a BTC lender on some of those exchanges and get around 20% APR since loans can be compounded every 1-2 days or even shorter depending on the duration of positions people open.

[jacksproit]

Is it legal for them to offer those services?

[LoSboccacc]

I think it heavily depends on their client country of origin. Here as long as bitcoin aren't officially recognized as bearer bonds of sort you can trade them around freely and the state only comes in questioning about plusvalences when you convert them back into money.