In a few areas one shopkeeper gives better prices for your goods than any other. For eg.
Targos: Elantra may be an enchantress but its you who has the advantage.
Underdark: Hegger Splitsteel can be scared into giving you a 20% markup on prices, both ways.

I want to know if you have come across any other such shopkeepers. Specially in Kuldahar and the Severed Hand.

Also, is it true that you are exported without your money? So a new game in HoF will see a band of grandly dressed paupers?

Finally, my bag of holding is filling up with just missiles and potions. Is any fight from the Field of Slaughter onwards so hard that I may need to use specific Missiles or Spell Potions? Or should I be not bothered and just use em up?

If you threat Bedoawn (sp?) to tell the Ten-Towns about his cult he'll give you a discount on his goods.

He's the werewolf cult leader you meet after you crashed, if you don't remember.

Beodaewn decreases his prices as compared to his original offer when threatened with exposure. However he still is a bad deal as compared to either Gnome.

Actually Zack Zoonsbury(?) might be the one giving you the best prices.

In Kuldahar, old man Conlan seems to have softened a bit with old age as he give you the most gold for your steel.

There's a dwarf in the Underdark (Hegger Splitsteel) who gives you a better rate if you threaten him.

Zack Boosebury gives reasonable prices for goods.

As for the missiles in your bag of holding, whether you use them or not will depend upon the make-up of your team and your playing style.