Proverbs 11:15

He who puts up security and guarantees a debt for an outsider will surely suffer (for his foolishness), but he who hates (declines) being a guarantor is secure (from its penalties).

The Bible tells us to help people, but not to let people take advantage of us. Not everyone is trustworthy, and in most cases, if they need someone to sign with them, it means they can’t pay the money back. We should decline to protect ourselves from paying penalties when they default.