The customer is liable for the order she placced: if she indicated the "wrong" product code it was NOT wrong: rather you performed your obligations and sent her exactly what she ordered. (It's the customer's responsibility to check her order before submitting it.) Legally, she should pay for what she ordered and you would not owe her compensation. Practically, if she's determined to fight, it is likely cheaper to send her the correct product while either letting her keep the wrong one or else having it call-tagged and returned (and you'd be entitled to charge her in that case); it's also better customer relations. (In the past, I owed a small publishing business, and that is what I did in similar cases.)