Can I charge extra because the customer is being rude to me?
Are you sure you can do that? If not, I will refer your store to the appropriate authority.
Thanks for letting me know.
It's wrong to charge someone extra because of their behavior since it is price discrimination and that is illegal. If you are experiencing a problem with a customer, you should try to complete a transaction as quickly and smoothly as possible in order to move on to the next customer.
You're right. I won't do that again.
It's not worth trying to get revenge on a customer as it would only lead to more problems and the possibility of you getting fired from your job. Deal with them swiftly and then you can forget about them.