Surely it is only unethical if you didnt do what it was you were paid to do...IE clean the carpet?
if a customer asked for it to be cleaned this way but you cleaned it that way, then yes, i can see the problem.
But as it stands, they asked you to do a job and you did it. It's not your fault that the carpet wasnt that bad to begin with and its not your fault that the customer liked your price and your service. If anything, that is to your credit.