1) Turn bet is too small. Obviously he likes his hand, and obviously that's a scare card. Just bet stronger and get it in. Why would you ever want to fold the nuts here when there is good odds, and very small chance you're being free-rolled (for only a couple outs at that).

2) Like $2.50 behind in $4.50 pot? Bet if he makes stupid calls, c/c if he makes stupid bets. Shove river if you check and he checks behind.

3) Eeek. I flat flop. He'll likely define his hands on later streets, and there are a decent number of cards that will give you a cheap showdown which you can take advantage of with position.

Villains don't tend to bet their draws, so best you're hoping for is 8x, 99-JJ, which will not usually bet that strong turn/river.