The calling station almost never bluffs. If they suddenly lead out or raise after being passive the whole hand, they have it. This is one of the most reliable reads in live poker.

Why they do it

Calling stations are defined by their passivity. Aggression is uncomfortable for them. When they override that discomfort and actually put chips in with aggression, it's because their hand is strong enough that they feel safe doing it. It's not a bluff. It's never a bluff.

The adjustment

When the calling station wakes up, fold everything except the nuts. Don't pay them off trying to be a hero. They showed you what they have.

What it's worth

Calling a suddenly aggressive calling station with two pair costs you a stack. One correct fold per session against this read saves $100-200 depending on effective stacks.