[Don Plumley]

The reality is you entered into a contract with the car dealer to buy a car. A final price was agreed, the contract signed, and goods exchanged for payment. The fact that the seller forgot to add a tax item into the total is their fault entirely. It's really no difference if they forgot to add in an option or simply didn't add right. A deal is a deal as some would say.

However, if the error was in the other direction, and you noticed they overcharged you $900, I imagine you'd be back in the dealer's office asking them to rectify the error.

So what to do? This is one of those, "what does the voice inside your head tell you to do?"