Don't confuse friendly with a vibe. Most men in the world are straight and tons are nice, friendly and outgoing. A contractor, checker or any other man being professionally courteous also isn't a vibe. I've hired them to work so I leave them alone unless they send signals and I'm attracted.
I look for the old standards: lingering eye contact, lingering smiles and eyes below my waist or blatantly undressing my body. When a guy is interested he'll let me catch his eyes running over me.
For example several years ago I hired a new pool service. It was a one man operation run by a student working his way through college. Instead of the usual machismo of limited eye contact he kept smiling and looking me over flagrantly. I returned his looks and smiles and it wasn't long before he was slobbering on my cock.
What works when a guy flirts is to flirt back the same way and see what happens.