I don't know much about the way real-world stocks work, but I've been spending more time on GTAV's stocks system than with the rest of the game, to get to know how it works.
Firstly, I mentioned in a previous post about being awarded $100,000 worth of Animal Ark stock by a guy whose motorcycle I rescued from being stolen (Search for my past threads for more info on that). Anyway, if you've come a little way in the game and have built up some decent money (I started this test with about $800,000), I've found you can invest that money in companies whose stocks are relatively cheap right now, and are still dropping, to actually cause them to go up. I can only assume this is one example of 'influencing the market' (I can also assume that if I'm using this term in the wrong context, that the endless supply of GTAForums trolls will correct me.)
In one example, I sold off all my AnimalArk shares. They hadn't moved in price since I got them, so I only got $101,360. However, I went back and reinvested that same amount back into AnimalArk, and whaddyaknow? It went up, within 2 minutes. Glitch, or suppose to do that? Seems like other investors saw someone buying up shares, and thought maybe I was onto something, so they jumped in. If it's suppose to work that way.
I could've cashed out after that 2 minutes, but it still kept going up. My profit amount wasn't going up very much, since I didn't have that much invested. Now, 5 minutes later, I could cash out and get an extra $87. Thats more than I had before, and had I invested my whole $800k, plus the $100k from the AnimalArk stocks I sold, that profit amount would've been higher.
AnimalArk wasn't really climbing fast enough for me, so I tried another. I went with ones that had the highest negative change, which at that time was Bullhead (except for LifeInvader, but I already know that's not gonna work.) I've been working this process on Bullhead for about a half hour while watching reruns of American Dad.
Save the game, then go buy stock from whichever one ya wanna experiment with (any will do). Note: You can sort each column by clicking on Current Price, Movement, % Change - for this experiment, I sort by % Change. Dump every dime ya have into that company, the more the better, then go back to LCN's main page (that shows the news headlines and cheesy graph.) Bounce back and forth between that page and My Portfolio till you see a change in Profit. (It updates maybe every 10 seconds or so, but you still have to leave the page and come back.) If you luck out, you'll see a positive profit in the right column, which represents the amount you'll make if you dump all stock now.
If it does show the stock went up and you made a profit, you can do one of two things right now: You can either wait to see if it keeps going up, which it doesn't always do! Sometimes it'll go back down, all the way down into the negative (meaning you'd lose money) - OR - you can dump the stock NOW, back out of the internet, and use the Quick Save on the phone. That gives you a "start over" point, which you'll use if things don't work out for ya.
And if things didn't work out for ya, all you'd need to do is reload the saved game and try again. Most times you'll get different (random?) results with the same stock every time. Like when I did the Bullhead stock, right after reloading, sometimes I'll gain $15,000 profit in 30 seconds, other times I'll lose $10,000 in 30 seconds. I can only guess it's random.
But if you'd rather just play the game, then you probably haven't even read this far anyway.
But if you DO like experimenting with GTAV's stock exchange behavior, I would say experiment on the stocks that have either a real low low or high negative change, then try the ones that have a really high or low positive change. For example, I tried "Slaughter,Slaughter&Slaughter" which was up 27% at the time, and grabbed about a thousand bucks of extra cash in 30 seconds. It wasn't going up fast enough for my liking, so I went back to Bullhead.
If you have a fairly large wad of cash to experiment with, and would like to keep the momentum going, you can modify your spending habits to "live off the interest", meaning spend only what you've earned through stock profits...this will ensure you have enough money to boost your profits in a fair amount of time. Even better, spend only half of what you earned in profits, using the rest to cut down the time it takes to earn profits...and it's a good idea to save yourself some 'emergency money' anyway, if it's your first time through the storyline.
Okay I'm done, bring in the trolls. I'm sure I've made enough spelling/grammar mistakes to keep those hopelessly bored children busy for hours. Any questions, google it, or PM me, because the kinds of comments you'll see below aren't worth my time coming back here to read.