dirty carpets in a big law firm
(NOUN) An idiom that's a 21st Century update of the old canard "canaries in a coal mine"; describes the warning signs given when seeing filthy carpeting and other shabby maintenance issues in a law firm, doctor's office, or other such business. Dirty carpets are a warning that the firm might be in financial trouble and could go out of business soon, since they are severely skimping on the basics that a successful firm would never neglect.
Jessica interviewed for a new job at a place whose office set off "dirty carpets in a big law firm" warning bells for her. Sure enough, two months later, that place was out of business.