Moisture Comes First, Always
Without moisture, mold cannot grow, which is why cleaning it up while the leak continues just resets the clock. Typical sources include a dripping trap under the vanity, bad window flashing, a bare-dirt crawlspace, or a bath fan exhausting into the attic.
A good remediation scope names the source and either includes the repair or tells you who needs to make it. When the cause is a plumbing or roofing problem, that trade often has to finish before remediation begins.
Dispatcher tip: Make sure post-remediation testing is done by an independent assessor, not the same company that did the work. Buyers and their agents tend to trust that report far more.