First, document what you're seeing
Capture the symptoms, prevent further damage where it's safe to do so, and note relevant history.
Then evaluate the whole property
Visible growth is a symptom, not the diagnosis -- the plan should also address water entry, humidity, material condition, containment, and verification once work ends.
Put the scope in writing
A written scope should define preparation, protection, materials, access, permits, testing, cleanup, restoration, exclusions, and change-order terms.
Compare proposals carefully
Verify credentials and weigh the reasoning and boundaries behind each bid, not just its total.
Confirm a proper closeout
Testing, cleanup, documentation, warranties, and remaining maintenance responsibilities should all be confirmed at completion.