Assuring Them
Despite the fact that they were really concerned about the unusual occurrences that were taking on in the house, they did not know if they would be able to reach her at this late hour. Upon her arrival, she gave them the assurance that the house had been cleaned and that the heating system was very recently installed.
Proof
The only thing that was required of them was to search the cupboard in the kitchen for the invoices. It was indeed the case that they were present. The evidence that validated all that she was claiming to convey. On the other hand, it did not resolve the mystery that they were dealing with at the time.