Lien waivers: get one with every payment

You paid the contractor. The supplier can still lien your house.

If your contractor doesn't pay a sub or a supplier, they can file a mechanic's lien on your property, even when you paid in full. In many states they send a preliminary notice first (California's 20-day preliminary notice): that's your list of who to collect lien waivers from. Get a conditional waiver with each payment and an unconditional one once the funds clear. For big material orders, pay with a joint check, and make the final payment only against final waivers. Rules vary by state, so check locally.