In vanilla Morrowind, your chances of using persuasion and the prices you get while bartering are made worse when your fatigue points are below 100%.

Is there a setting in the Construction Set where you can turn this off, or is it hardcoded? The mechanic is realistic, but having to wait before attempting to barter or persuade to achieve optimal chances is just annoying.

This would be a trick to mod. You could look at some of the economy mods to see if anyone has changed this aspect (IIRC, they have not). The Morrowind Code Project is the only one I know of that fixes the Disposition Bug, so it may be buried in the code of the game.

Two workarounds would be a method to restore Fatigue (spell or potion) or that would boost your Mercantile to 400 for like a second so the Merchant accepts any offer you make.

Another work around is to wear the Boots of Blinding Speed. They make you so fast that you never have to run and reduce fatigue.

Ah, OK then. Since I am absolute novice modder and there is no simple off switch in the Construction Set, I'll drop it.

On workarounds, I have plenty of workarounds! Pressing T and clicking "Wait" is instant, but it's still an unnecessary hassle.