The hotel where we had our wedding reception just sent us a notice that they miscalculated the final charge and left off sales tax/service charge. Comes to a thousand dollars. Legally, we are under absolutely no obligation to pay it - the invoice is marked final, says "sales tax/service charge included", we would have no way to reasonably know of their mistake, etc. It's a classic contract law fact pattern. However, ethically, we agreed to pay the charge and if we'd've scrutinized the invoice, we would have caught the mistake (even though we had them confirm the price twice). So while I don't have to pay, I'm going to pay it. Even though it is Marriott Inc. I'd be screwing over, I'd still be screwing someone over. It just sucks. That's a good chunk of change.