In Frontlines, I commend players with the highest Battle High.

In CC, the player that died less and contributed more, or successfully called shots.

In Normal content, to the player that helped me as DPS more.

About commendation begging: LOL

That's something that comes naturally by playing the game, a person that asks for "compensation" is probably being chatty and acting nice as a means to an end and that's gross.

+ 1 to the stamp idea, that's really neat!