How do I know this guy is saved?

Of course, I understand that we cannot really ever know if a person is saved - God separates the wheat from the tears.

But when you are sharing the gospel with a person, what are you looking to see/hear/observe to know that a person seems to be a believer? I think of the story in the book of Acts (8:26-39) where Philip is sent to an Ethiopian eunuch. He decides that the person should be baptized, thus recognizing him as a believer -- what do you look for to recognize someone as a brother or sister in Christ?

Christ is all-