Some of these approaches require short selling stocks; the trader borrows stock from his broker and sells the borrowed stock, hoping that the price will fall and he will be able to purchase the shares at a lower price, thus keeping the difference as their profit. There are several technical problems with short sales - the broker may not have shares to lend in a specific issue, the broker can call for the return of its shares at any time, and some restrictions are imposed in America by the U.S. Securities and Exchange Commission on short-selling (see uptick rule for details). Some of these restrictions (in particular the uptick rule) don't apply to trades of stocks that are actually shares of an exchange-traded fund (ETF).

In addition, in the United States, the Financial Industry Regulatory Authority and SEC further restrict the entry by means of "pattern day trader" amendments. Pattern day trader is a term defined by the SEC to describe any trader who buys and sells a particular security in the same trading day (day trades), and does this four or more times in any five consecutive business day period. A pattern day trader is subject to special rules, the main rule being that in order to engage in pattern day trading in a margin account, the trader must maintain an equity balance of at least $25,000. It is important to note that this requirement is only for day traders using a margin account.[20]
The bid–ask spread is two sides of the same coin. The spread can be viewed as trading bonuses or costs according to different parties and different strategies. On one hand, traders who do NOT wish to queue their order, instead paying the market price, pay the spreads (costs). On the other hand, traders who wish to queue and wait for execution receive the spreads (bonuses). Some day trading strategies attempt to capture the spread as additional, or even the only, profits for successful trades.[18]
You're probably looking for deals and low prices, but stay away from penny stocks. These stocks are often illiquid, and chances of hitting a jackpot are often bleak. Many stocks trading under $5 a share become de-listed from major stock exchanges and are only tradable over-the-counter (OTC). Unless you see a real opportunity and have done your research, stay clear of these.