So:
Kattar and Alicia: (Damsel in the Red Dress)
Neither one of them compliments each other a lot on their physical appearance. Alicia, a bit out of annoyance, because girls are always gushing over him, and have since they were in Junior High. On Kattar's part, it's out of awkwardness, and wariness to scare her away or be rejected. I mean, when you practically live with your best friend it could ruin everything if the feeling isn't mutual, and he's terrified to death of that idea. On the other hand, he compliments her constantly about her talent and genius, trying with everything in him to convince her she's "got this" and has what it takes to be legendary someday.
Jinwoo and Kimberly: (Hushabye Prince)
Kimberly will give subtle flirtatious compliments, but she's not the type to say things overtly, as she's trying to feel Jinwoo out, and he's pretty hard to read. Jinwoo will give compliments to his little sister all the time, because he's not worried about scaring her, but with other people, he's wary, and opts toward staying quiet if he's not sure how what he says will be taken.
Aaron and Eliza:
Flirt all the time. Basically non-stop. Also complain about each other, but they have no shame in giving each other compliments. Why should they? They've been married for 9 years.