1. Note what you're seeing and hold the line
Write down the symptoms, take steps to stop things from getting worse where that's safe on your own, and pull together any relevant background on the house.
2. Look at the house and the site together
A stain or musty smell is only the visible piece of it. A plan that actually works accounts for how water is entering, ongoing humidity, the condition of the affected materials, containment during the work, and a way to confirm it's fixed afterward.
3. Get the scope in writing
Nail down preparation steps, what gets protected, materials to be used, access needs, permits, testing, cleanup, finish restoration, what's excluded, and how change orders will be handled.
4. Weigh providers against each other
Check credentials, then look past the bottom-line number to how each provider explains their reasoning and where their scope starts and stops.
5. Walk through closeout
Before calling it done, confirm test results, cleanup, documentation, warranty paperwork, and any maintenance that's still on you going forward.