The Liberty City National (LCN) Exchange is GTAV's offline stock market that is not affected by Rockstar Social Club online actions, and can become a very useful source of income. The idea is to purchase stocks when they are as cheap as you can make them, then sell them off when they return to high values.
To manipulate stocks, you can hold up specific companies or continually destroy vehicles of a particular make to reduce their value. Purchase the stocks when cheap, then do the same for rival companies/makes to force their value back up again.
Assassination missions provided by Lester are often closely tied the stock markets, as bumping off targets will have an affect on the value of their companies.
LCN Stock Market Rivals
CoolBeans vs. BeanMachine
Burgershot vs. TacoBomb
FlyUS vs. AirEmu
GoPostal vs. PostOP
Bilkington vs. DollarPills
Pisswasser vs. Logger
MazeBank vs. BankOfLiberty
Redwood vs. Debonaire
Slaughter, Slaughter, Slaughter vs. Bullhead
RadioLosSantos vs. WorldwideFM
eCola vs. Raine
