I would take a breath and buy a $4.99 polarity tester from any harware store or Home Depot:
One of your neigbors probably have one, 2 second test if the electrician knew what he was doing. Beyond that a DVM would confirm there is'nt some strange luner issue like in the movie "Frequency" causing crazy voltage swings
Unlike automotive electronics there realy isnt any black magin in AC wireing, its very simple but people screw it up often.