Depending on whom you ask, ratings agencies are either would-be guardians of financial probity or an indispensable valuation tool for investors.Their reputation was badly tarnished by the 2008 financial crisis when critics said they failed to notice the warning signs in over-extended banks.But since then, they have tightened up, promising new rigour in their analysis of government and corporate finances to ensure investors make the best-informed decisions possible.Their actions - like S&a