I dont think he will do it again, and as I say, I can make a plan, either with a polarised connector , or better still an enclosed ( to avoid corrosion in the tropics ) relay to only connect with the right Polarity.
I will fix up the units, and the guy will owe me BIG time, and his boss will be grateful to me, so what the heck, I dont want to get all grumpy about it 