"We should make Merchants refuse to re-buy their own shoplifted items" -- Can't be done.

However, it's easy as pie to fix the "Gorch Exploit:" None of the stores are hard-coded, so it would be a simple matter to check the flags in the various *.STO files, and make sure that NONE of them will both allow shoplifting and purchase stolen goods. Some may allow one form of theft, and other stores may allow the other, but NOBODY will let you do both.

Drow items are commonly known for their buggy class restrictions. If you want to see Cernd using Longswords, Flails, and Crossbows, Ust Natha is the place to be.

Bernard doesn't have infinite prismatic spray scrolls. He has 14. (I stole them all, just to see how much he has)

[offtopic]

Chapter 5 and 7 spoilers...
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already a spoilerish topic, but I wouldn't be performing at peak performance if I didn't warn you...
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Anyone remember Matron Ardulace's comments when you go to see her the first time, about how your party looks slightly different? I thought it would be funny to have my party wear their normal gear instead of the drow stuff and CLUA in some chickens, pheasants, squirrels, groundhogs, cows, horses, and bears. Yeah, we're not the typical drow warriors!

[/offtopic]

AFAIK, the Suldenessellar priestess also sells for more than she buys. Pre-patch, of course.

ToB spoilers (highlight to read)
*<font color=#3D2F1B>There are also some bugs in the Smuggler's Cave. I could sell a leather armor and a few scrolls for more than the smuggler sold them to me. Not much of a price difference to rake in the gold, and didn't work with all my items (I tried). Game was patched and Baldurdashed. Weird.</font>*

Pirengle, the ToB price differences you mention sound like "No-stock" issues to me. "No-stock" is where a merchant does not already have any of X item, so he assumes that X item is rare, and will pay more for it. This gets particularly ironic in ToB, as so few of the merchants carry non-enchanted items, so you can easily sell a Composite Longbow for 60gp--whereas Ribald would only pay 15 for it.

I exploited this just today--gleefully abusing the Unlimited Bag of Holding, I weaseled over 600,000 gp out of Karthis al-Hazzar. (As if I needed the money.)