I've seen a few Google results on this on the internet but none are properly answered, so let's try and sort this.
First, the markets.
Now, as far as I'm aware, BAWSAQ is affected by the actions of people online, and LCN affects the single player story mode only.
On the first assassination mission for Lester, he says to buy stocks in Betta Pharmaceuticals, which is on the BAWSAQ market. I checked the stocks, and they were showing down 0.66%
I asked my friend and he said they were exactly the same price for him.
Now, I'm playing again today and they've gone up 32%
How can Lesters missions affect BAWSAQ stocks if they're the same for everyone online?