To expand on Kerenbron's advice:
Because of the way I play (solo) Haggle is practically a necessity. To become an expert while still in the first town, here's what I do:
1) Not everything is salable; some items are intended only for use as a tech component. (Rags, charcoal, broken flintlock, etc.) Go through garbage cans; there are salable (and non-salable) items to be found.
2) Invest a point in Haggle. Gather up 100 or so gold, to buy apprenticeship from the general store. Sell whatever he'll buy: wine, bullets, shoes, potions, clothing, etc. Nobody but the junk dealer will want your flints and springs... yet.
3) Gather up another 500 gold, with which to buy expertise. Sell what you can to the blacksmith: armor, iron ore and steel (or pure ore), weapons, etc. (Note: do not sell magic weapons unidentified, except for daggers. Identification costs 100 per item, from the gypsy near the bridge thieves.)
4) Help Doc Roberts with the bank robbers. (Pay for apprenticeship in your attack style of choice, if you can afford it.) Afterward, strip them and the dead guard; sell to the general store.
5) If you still don't have enough gold, try the temple, the mine, and the unlocked rooms at the inn. Once you've hit your goal, the inn's bartender will train you. (You need 3 points in Haggle; I "cheat" by playing a gnome, so that I only need 2 points and 9 WP.)
6) Profit! :D
If the above sounds like too much work:
In general, stores buy what they sell. Junk dealers buy anything salable, but at a much lower rate; if they won't touch it, nobody else will either. (Except for arrows, and possibly bullets.) All chests at all inns are safe to use as storage; despite the fact that you can take anything you want, nobody will steal from you. Don't over-stress about cash; unless you're planning to buy a mansion and a yacht* you'll pretty much have enough money for whatever you need by the time you finish exploring Tarant.
Haggle expertise allows you to sell anything salable to anyone. In Shrouded Hills, the Herbalist gives you the best rate (and is the only one willing to buy arrows); in the cities, this isn't an issue. If a merchant runs out of money, go at least a full screen away and "sleep" until the next day.
One final protip: Don't trade the camera; you'll regret it later. (And after you trade the boot, buy it back; there's a place in Tarant willing to give you a much better deal than that cheapskate Ristezze.)
*Both of which are possible, though I'm not going to spoil the game by telling you how here.
Post edited June 03, 2013 by TwoHandedSword