That guide is for the online game and doesn't really pertain to the handheld version at all. All you need to know is buy low and sell high. It's all about making money. Buy a bigger trenchcoat when you can as each one adds 10 pocket space. If you get the chance to buy a gun, don't bother. Only purpose is to shoot back at the cop and in my experience he's a MUCH better shot than you, so just run away. Also, pay back your loanshark asap because the interest is horribly high. But make sure to only do it so you'll have some money left over. Otherwise you'll have no debt, but no cash to buy drugs with.