Just some information which may help. Sorry about the long read, but worth knowing. Some people already know this, but im sure a lot dont know.
Market Makers are able to short stock, this can lead to price manipulation. You may not know it but some of this is naked short selling or even legal short selling using your own shares against you which can lower the stock value and adversly affect your investment, Market Makers do this by "borrowing" shares to cover their shorts, your shares possibly. The only place Market Makers can borrow shares from is other Market Makers or brokers and guess what brokers have plenty of - thats right, their clients shares - your shares. Why would you want your shares loaned out to use against you and adversly affect your investment while the Market Makers use those shares to make money for free off of what you paid for? This is common in penny stocks (although naked short selling is illegal it still happens frequently in penny land). The solution may be to make sure your own shares are not used against you is to tell your broker in writing to not do this, it is your perfect right to do as they are your shares. If all share holders would do this the supply of free shares available to Market Makers for shorting would dry up, then they would be forced to actually buy their shares and do a lot less shorting and as a result a lot less price manipulation. A lot of brokers will tell you this is not a problem and they do not do this, however, behind the scenes they will do this and without specific denial of permission in writing from you they can legally loan your shares to Market Makers. Also heard that a high sell order will prevent this from happening.