What is a vendor lesson you learned the hard way?

Every property manager and board member has at least one — the vendor that came in cheap and walked out expensive, the contractor whose change orders ate the project budget, the licensed pro whose license turned out to be inactive when the claim landed.

What is one thing you check now that you did not check on your first hire? What changed between job one and job ten?

Mine: COI from the agency, not from the contractor. Took one year and one denied claim to internalize.