Salesperson misquoted price. Do I have to pay back the difference?

Question

Background

I purchased something from a local store. The salesperson made a mistake and quoted me a lower price than what should have been. I made a down payment since they didn't have what I want at that moment. A week later I paid the remaining and got the goods I asked for. Days later, the same salesperson called me (I left my number with the down payment), saying he under-quoted one of the few items. He asked me (with good attitude) to pay back the difference. I decided to be a good guy and deposited the difference to the store's bank account.

I though wonder if I am legally required to pay them back.

Question

In the case that a salesperson made a mistake and gave an underpriced quote to a customer, after the service had been served or the goods had been delivered, and the customer had paid in full, can the salesperson (or the store) legally demand the customer to pay back the difference?

Answer 1

In general, no.

When the salesperson quoted the price and you accepted it you were each bound to that price by contract. Consideration under a contract must be sufficient (something of value for something of value) but it doesn't have to be fair: you can be obliged to pay $2 million for a cupcake or sell your Picasso for $1. You were and are under no obligation to pay and could successfully sue for the return of your money.

To further clarify, it doesn't matter if the store has or has not provided the goods or services when they discover their error: they are obliged to perform their side of the contract without additional payment.

Further, if this was a consumer contract then some sort of consumer protection law almost certainly applies. This would probably make what the store did not only a breach of contract but an offence against the state as well.