Remember beside the cost of “borrowing” shares when you sell short (which you are legally obligated to do), you can wake up any morning and find out that the shares you borrowed are no longer available to you (not your choice), and you are required to immediately buy back the shares you sold short. This of course could happen when the stock is higher than what you received, so you will incur a loss. Moral:- selling ain’t for the weak at heart.
There are many additional industry rules affecting short selling when compared to purchasing a stock long. The prior message from sshapiro is on the mark in regards to the possibility being bought in at anytime. We do work hard to avoid this, however in a situation where a security is no longer available to borrow to cover a short position a buy in would occur. Take a look at the following link it give a pretty comprehensive review of the strategy of short selling.
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There are rules that govern investing. You appear to be new here. On the chance that you are also new to the investing world, let me add, if you trade without a knowledge of the rules, you limit your ability to succeed. It would be like playing checkers without knowing that you can only move backwards, once you have a king.
With your experience level maybe that is a better place to start. There is no risk beyond that of buying an equity, but you will need approval to trade options. It's either level 1 or 2 I can't remember.
Margin is trouble you do not need in your life as a beginning investor.