1)
Why did they say that David does not want to honor Chanun's father?
1.
'Rashi', from Tanchuma Pinchas 3, Rashi (Shmuel II, 10:3): David's Torah says "do not seek their benefit or Shlomo, forever" (Devarim 23:7) - would he abandon his G-d's Mitzvah and seek your Shalom?! Surely it is to spy the land!
2.
Malbim (Shmuel II, 10:3): They did not come like those who come to make a Bris with the living king, like Chiram sent to David and Shlomo.
2)
What is the meaning of "v'Lahafoch"?
1.
Radak (Shmuel II, 10:3, citing Targum Yonasan): It is to examine. One who examines something, he turns it from side to side.
2.
Malbim (Shmuel II, 10:3): To [conquer it and] convert it [to become part of Yisrael].
