Purchasing a refurbished property

Addrianne

We are currently negotiating to buy a house which has been refurbished. A private builder completed all the work. The guarantees for the heating and newly fitted flat roof hold the builders name. We are led to believe these guarantees aren’t worth the paper they’re written on.
How can we protect ourselves ? Can the Vendor provide an additional policy from a reputable insurance company to cover the work carried out. ?