Is it legal to sale a home with black mold under carpet?

Local laws vary on real estate. You will need to check the local law on that one and under what conditions you can sell it. In this state it is legal if it is revealed.

(I know of one man who had it. The man who purchased his house wanted to tear it down and build something else. It did not bother him that he could not have gotten a c.o. for it.)