] And, why would she be willing to accept his word on face value - simply because his manners were all politeness and he was so agreeable? I would think that the old art (as described by Caroline Bingley) of making another look bad so as to make yourself appear superior would be something Elizabeth could recognize immediately.

I like to consider myself a reasonably intelligent woman, and I can confess to having made a leap of logic (or faith?) very similar to Lizzy's, here. From her point of view, as I see it:
____________
" Darcy was rude and hateful at the assembly and insulted me directly.
While I was caring for my ill sister, we had some very bizarre conversations, and he was rude to me again (I maintain that she thought of the "don't you want to dance a reel" bit as a direct insult).
The whole last day I was at Netherfield, he was uncivil, he sat with me for better than half an hour once without speaking.
He stares at me, and eavesdrops on my conversations. Why? He must find me really abhorrent.
Well, (nyah) I find him pretty darned abhorrent too, so there.
But wait, Bingley likes him, and Jane keeps making excuses for him.
So it isn't satisfying to talk to my usual confidante, Jane, about how horridly proud and arrogant Mr. Darcy is. Well, then, I'll keep it to myself.

*fester, fester*