if the fans were working when you sent them out then it's probably the sparky who's fooked them or it's anotehr problem with the wiring

i'd he'd stayed calm and all that i would have problay said explain to him how to wire them up and if they don't work, as long as he woas willing to pay for the postage back, you could possibly send him out anotehr set

but seeing as he's being an arse about it, i'd tell him that they were working when they were sent out to him, and if it's the same set of fans and they are now not working, it's his sparky thats fooked them
then tell him to send them back at his cost to have a look at them
and then see if they work or not