Monty's Motor Sales sold a mobile home to Hornbacher. Before the written contract was signed, the salesperson told Hornbacher that Monty's would take care of any problems that Hornbacher might have with the mobile home. This promise was not included in the written document. When Hornbacher had problems with the mobile home, he asked Monty's to take care of them. Monty's refused to be of any assistance.

What is the legal concept(s) being discussed?