The help you ask for should not require someone to violate another promise to provide it.

A request can put somebody in an impossible position without your realizing it. Covering your shift means breaking a promise at home, lending you the money means breaking one elsewhere, keeping your secret means lying to a person they care about. They may well say yes and pay a cost you never see. Help is only clean when it does not require a hidden betrayal.

When you ask, say plainly that a no is fine and check whether it clashes with anything. If it does, withdraw the request rather than leaving them to choose.