I WANT to understand the "market information" as much as the next guy. But even after I follow the walkthrough and get the chick to start handling it, and get her revised screen, I don't get how I am supposed to pick which cargo to buy each iteration. Can someone explain how this works?
		
		
	 
Ok, sure.  BTW, have you clicked on the big "?" in the menu at the top of the screen? There is a quick overview of the whole process there if you'll just blow up the pictures and read the steps.
In the meantime, after Tiffany is helping you buy and sell, you get this very informative report that lays it all out clearly. See your credits in the upper right? That's your budget. See your location in the upper left? That shows you which column you have to buy from. It's color keyed and always on the left column. You pick the commodity and the quantity based on what you can sell it for as shown in the other two colored 'sell' columns on the right. You choose your next destination based on where you can make credits.
For example I've shown, note that since you're in the Pleiades Sector you could buy Grain for 37.4 credits and sell it for 38.2 at Orion station. But if you went to Beehive next, you could only get 34.7 for grain and you'd lose credits. IF you buy Protein you earn at both station but more at Orion.
But you can buy anything in the left column you want!  And this Market Analysis shows which one make you money at the other two stations and which do not. For example if you bought Beryllium here at Pleiades for 127.2 you'd lose money at either of the other two stations. So reading this panel tells you what to buy.
Then when you get to your next station, the first thing you do is sell your inventory to see how much your Current Balance when up.  
So its a case of buy cheap here and sell for more there and make money so you can buy that scanner to go and start scavenging and make even more. 
Again, click on the big "?" and it's all laid out there too. 
Best of luck, Captain....