As far as I can tell, FCC (v.1.07) is wrong a fair amount of the time. Specifically what I think is happening is that he loaded all the specific base Buy/Sell info into his database -- things that are specifcially mentioned as being bought and soul, such as when you do the "?" on a base in the F6 map -- and he set everything else to "default" prices. (The prices you see in parentheses after the item name, in FCC.) However, it looks like the game actually has a far greater number of "non-default" prices than the ones shown in an F6 query. Specifically, if something can be bought cheaply nearby, it is almost always lowered in all other bases in the system, and even nearby systems.
This was all a long way of saying that, as far as I can tell, FCC is often wrong when it shows a Buy or Sell price as equal to the Default price (seen in parens after the item name). It's often correct, too, but you won't know until you check it.
You can see "correct" prices inside the game for any base you have visited, in the Description along the bottom of your screen when in the Commodity screen. Also when you bring up the Inventory screen (F8), you get an even nicer Description under Trade Values, which is sort-able etc. However a big drawback for both of these, is that you have to have the item in question present (either on Commodity screen or in your hold) in order to get these Descriptions. Also you will only see prices at bases you have visited, although all you have to do is pop in and out of them for a moment.
I wish that the FCC author would post an update to his nice utility, or otherwise mention if something is going on that we're both missing, in a README. I'd hate to be calling his program busted if it's really my bad. Actually, it's hardly totally busted... it's just wrong SOME of the time, and that's a hell of a lot better than having no utility, since there's otherwise so many zillion possible runs. Just be sure to check that the prices are for real, if they are equal to the default prices
-- CAPT H