In my experience a pick pocket skill of around 170 will let you thieve to your hearts content. There are one or two exceptions. Bernard in the Copper Coronet is one of the most difficult people in the gameto dip and he will eventually catch you regardless of your skill. The gnome merchantin the Umar Hills is another difficult sod.
Dexterity plays a major role in your thieving ability as does the armour you're wearing. Elves with high Dexterity make excellent thieves as do some others, halflings I think. Try to drink a dexterity potion and remove your armour prior to going shopping.
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It's bleedin dark down here, slippery too.
Man, that's a pisser.
