What do you think about me keeping the extra dollar the cashier gave me by mistake?
Are you sure you want to keep it?
Yes I'm very sure.
It was a mistake but you shouldn't keep the money. It doesn't belong to you and the cashier will get in trouble.
I'll probably just spend it... do you think it's wrong?
I think it is wrong, and I think that most people will think it is wrong. It wasn't your money to keep, give it back.