I often have to distinguish whether someone is speaking 반말 banmal or 존댓말 jondaemal. Usually I pay attention to the ending, if I hear a -요, -니다 or -니까 I assume it's jondaemal otherwise banmal, but I'm not sure if that's always the case.
Are there any other rules to recognize one or the other without actually knowing all the vocabulary used? Is it possible for sentences to be both at the same time (neutral)?
Real life example:
A: "[...]에서 왔어요." (jondaemal)
Person B didn't understood properly where person A came from and asked
Did person B really asked in banmal or is this neutral?
Note: I know there are several levels of politenes, but I mainly care for those commonly used in modern days conversations. Thank you.