One thing I like about the stock market is that in it there is never a dull moment. Especially in highly efficient markets, any new day or each passing minute promises renewed market activity as new  information is quickly absorbed and reflected in stock prices.

As securities engage in the 'random walk', market participants jump into action to squeeze profits out the emergent price volatilities. Stiff competition therefore becomes a common phenomenon, something that  is both expected and encouraged under such high pressure environments. The peril however crops up in way of market participants engaging in unethical practices to get ahead , earn favours or make unusual profits.

Luckily, in most markets regulations are put in place to render some of these practices illegal.In most stock markets,the following practices are considered illegal.

Insider Trading

In most semi effient markets, information that would affect a stock's price takes a while before it is  reflected in a stock's price. This period,opens a window for individuals who have this information before it's made public to take positions that would favour them. This is called insider trading and it puts others not privy to the information immediately at a disadvantage.

Marking the Close

The forces that determine prices in most markets, the stock market included, are the forces of demand and supply. However,this forces can be artificially created or manipulated to bid up the prices of stock just before the close of a market.Something referred to as 'marking the close' in stock market lingo. As mentioned,It involves creating artificial demand for stocks owned by placing orders for them at a higher price than they're trading. However since markets are efficient, the stocks drop to their previous price thereby causing other investors that might have followed the herd to make major losses.

Squeezing the Float

A float as regards to the stock market is the total number of shares owned by the public that are  available for trading. In some instances, shortages of such stocks arise, making way for unethical market participants to control the demand side and thereby exploiting the market to create artificial prices. Thereby making the prices to moves upwards as the demand becomes more that the supply. The prices thus created due to such manipulation are highly inflated making the stocks  risky to purchase due to capital losses thereafter.

Front running
Just like Insider Trading, Front running involves the use of information held before it's made public/available to other concerned parties in such a way as to derive benefit from it. But in this case the term is limited to brokers and the concerned parties are its clients. Normally, the broker or brokerage would take a position on such stocks using the information they have before recommending it to the client who doesn't have that piece of information that supports that position yet.

Hype and dump

Also referred to as 'pump and dump' it normally takes  two stages to manifest. The first stage involves the owner of the stock spreading false information that would influence the prices of the stock to rise thence the 'Hype' or the 'pump'. Since the price reached will not be a stable price the next stage which follows immediately is selling the stocks to avoid making losses its prices start to fall hence the 'Dump'

The implications of these practises is that sometimes the market prices are not what they seem to be. The practices outlined are illegal but they can cost you a lot of money before they are detected. Thence, coupled with some deep study of the market, I'd  advise you to always go with the buffet rule 'Be fearful when others are greedy and greedy when others are fearful.' It helps.