Q: I bought
some used gold,
then I refined it in a way to make it look like new before selling it at the price of new gold. It should be mentioned here that I did not inform the buyer about this. Is this sale permissible?
If the case is as you have mentioned, it is impermissible, for it is a form of fraud.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.