I hated it when i accidentally gave a lot of stuff for free to a random trader thinking she will pay me automatically.
Making mistakes is annoying but:
a) Move your quicksave slider to 25 in the options window
b) Save a lot--if you had a quick save you could have reloaded
c) Don't make that trading mistake again, there's no reason for that to happen twice
I hate it when i have to choose the right amount of gold to trade with that clumsy slider thing.
You can click the balance/scale at the top of the trade window and it automatically adjusts the gold for you.
You're welcome.

About 1/3 of your complaints can be mitigated with quicksaves, too.
Agree with the poster above, the game feels like old-school D&D to me.