Most of the evil BG1 characters are so very subtle about being evil, too. Who are you thinking of, now? The crazy necromancer? The Red Wizard who talks to himself and insults you constantly? The psychopathic halfling? The drow priestess of Shar? The misogynistic con man? Name one evil BG1 NPC who a PC who wasn't stone deaf and stone blind could possibly avoid knowing was evil.
But what about a PC with an int and/or wis of 3? He'd barely be able to remember his companions names, let alone able to understand and remember their personalities.
Regardless, talking to yourself, being insane, eager for a fight, prejudiced, rude, arrogant, sexist, selfish, greedy, or just generally obnoxious are not traits that automatically makes someone evil. In fact, at least five of those traits can be prescibed to Anomen! A large number of good and neutral NPCs in both BG1 & 2 have at least one or two of those traits as well.
To me, Eldoth does not come across as evil at all. Sure, he may only be interested in making money, treat women as second class citizens, etc but how is that evil? Even a lawful neutral character could be like that. IIRC he doesn't once express an interest in murder, rape, torture or any other kind of genuinely evil activity.
Regarding Viconia, if you'd never even heard of Shar/were too stupid to understand what she was about/forgot what you'd been told/knew that some of her priests are neutral, and/or weren't prejudiced against Drow, Viconia wouldn't come across as particularly evil either.
Faldorn comes across as far more evil than either of these two characters, yet she's true neutral.