Because the OP said she talked to him about it. If he didn't know about it, wouldn't he have said something instead of explaining why he had to pay it?Only a court order would authorize the employer to garnish wages, but I don't see where it says he knew about the court fees, etc. Maybe he missed the court summons while ignoring calls, collection notices, whatever.
OP: Do you know if he fought this in court?
And, then again, maybe he did try to scam the buyer with faulty equipment, not something the IT guy would admit.