I've come to the same conclusion. I just came across all this, and tried the following:
1. Edit the shop.dat file to get a multiple of the same item already in the pharmacist shop to appear. (success)
2. Buy one of the new edited items (success)
3. Put an item from the blacksmith in the pharmacist shop (success)
4. Buy that item (fail)
5. I went and tried changing the store Type from 5 to 2 (pharmacist to blacksmith which is what the item i had in there was originally from) (uncertain*)
6. Tried to buy the blacksmith item again (failed)
*uncertain that it worked because it didn't yeild any results. however the value i changed seemed to be the correct one and i didn't get any errors. it was the 5 before the 19 in the shop.dat file.
my conclusion is that it is impossible to hack items into the shops AND buy them without tricking the server in conjunction with editing the dat files.
- Steve
P.S. that screenie kitsune posted of the fire work in the pharmacist shop looks mighty familiar to the one i sent her a long time ago.