[shootaa]

i think the fact that villain could have a busted draw 1/7ish of the time (which is think is pretty close) and/or is making some sort of play/thin value bet at this, paying off the river and feeling like an idiot doing so in situation 1a which is more apt to be a semi-bluff than a trap (for fear of pushing you off a smaller pair). 1b is a little more borderline i feel like, and i like your approach here, absent any ace or king, i pay off.

for 2a and 2b, i usu call down not matter what absent any read.