Dialogs in Morrowind currently implement a temporary disposition for each instance solely for disposition changes during bartering. This setup would kind of make sense to stop spamming 1 gold transactions, but considering how tedious that task is, it doesn't really need a deterrent. Instead, we have a system where there is no penalty for haggling. You can simply use your personality or wallet to boost disposition once, and reload the dialog window to recover from those 40 or whatever failed attempts the transaction before.
MCP handles this issue by allowing users to make them permanent. Users could then optionally set a gmst to disable the disposition increase to fix the game play exploits it introduces. OpenMW could take it a step further and base the disposition increase on whether the transaction was profitable to the merchant. Then there would be no benefit to spamming 1 gold transactions and you'd have the choice to haggle for a better deal and gain mercantile experience or get easy money and a better standing with the merchant.