You can't put "no returns" to cover (undeclared) faulty or SNAD items; it's just covering goodwill returns.
However, I'd say the listing was pretty clear that it was just the flightcase and the misunderstanding was on the buyer's part.
I'm 2/3 of the way through my current GAS list:
I bought a Rickenbacker 5-string last month.
I bought a Kramer aluminium necked bass yesterday.
I would like a Status Graphite headless 5-string.