More context is needed. If standard written English, then it should be "somebody lookS gooD." If quoted speech, then the author may be approximating a character's nonstandard speech.

I agree it’s impossible to say for sure from that. It might be a typo for good. sb is often short for somebody, and that would make a comprehensible sentence, albeit extremely informal and improper. I’ve heard similar used as a compliment: “Ooh, sb look good!” Sort of short for Sombody (i.e. the person they are complimenting) is looking very good.

Text dialogue, it is impossible to read wrong.

This makes no sense. Perhaps you misheard the person.