Standing surety for someone

A guarantor undertakes to pay if another person does not. A referee puts their own name behind a stranger's application. In both cases what makes the undertaking worth anything is that somebody with something to lose has attached it to someone else's conduct. Credit models price default better than any guarantor's intuition, and this register has already handed scoring to the machines. Surety is a different act. Common law and civil law both build it as a promise by a person who can be pursued, and the creditor's remedy runs against that person rather than against the assessment that led to the loan. A model will tell you the odds that someone repays. It cannot be the one who pays when they do not.