So far every time I use the assess local prices option it gives me 3 good that aren't available. Is this supposed to happen? I've got my trade skill up to level 3. On Warband at level 3 I only got goods that were available in that location.
Yes, that is how it is coded, at least in Warband.
You get a random chance, based on your Trade skill to acquire better and better information. Sometimes that random chance gives you garbage.