Baldur's Gate Enhanced Edition

[ThiagoMartell]

While having to pay more when your rep is low is stupid and nonsensical, (...)

I really don't think it is.

I think it's more that you get a high reputation for helping people, so shopkeepers don't mind giving you items at a discount. At lower reputations (but not low enough that the Flaming Fist are constantly attacking you), they don't have any reason to do you any favors.

Besides which, if a shopkeeper is overcharging you, the Evil thing to do would be to steal what you need anyway. ;)

This is the official version. IIRC, the manual even mentions it as 'the hero discount'. If that is not enough for you...

Also, with low reputation, you might be paying them a bribe so they won't set the guards on you, a known criminal.

Not liking something is one thing. Calling it stupid and nonsensical... that's a very different thing.