The term guarantee is from the 1670s, "person that gives security," altered (perhaps via Spanish garante or confusion with legalese ending -ee), from earlier garrant "warrant that the title to a property is true" (early 15c.), from Old French garant "defender, protector; warranty; pledge; justifying evidence," from a Germanic source, from Proto-Germanic *war- "to warn, guard, protect."
A guarantee in business is a powerful tool. Not enough businesses use them to their advantage. Stand behind your product or service. It keeps you competitive by keeping you on your toes because every customer has the potential to walk away. Focus on quality and service.
Grant security, pledge a forward warranty, protect and defend