I noticed that in some shops (and I've only had experience with ones in Rivermoot) the shopkeeper's inventory gets kinda large with several duplicate items.
In other NWN servers that I've been in, this tended to contribute to lag.
My suggestion is to implement a cleaning script that would remove excess items until there are only 2 or 3 of the item in the shopkeeper's inventory. Or something similar with the purpose of reducing redundancy in the shopkeeper inventory and to reduce lag.
I do like that treasure loot items are available in the store via other players. I think it's great and realistic, but would the merchant really have 35 garlics on display? (ok, bad example

) Just a suggestion to help keep the server cleaner.