If he talks to you everyday. If he asks what your plans are or asks about your family, that is a pretty good sign. On the other hand, he might be leading up to talking to you about a business opportunity (Amway).
Sorry, dear; It's NOT a fine line between having a gentleman be socially polite to you ... or being "hit-on". Presuming the man in question is an adult: if he wanted to get you into his life (& his bed), you'd know it. Think about it.