Most commercial cleaning disputes trace back to one thing: a scope that was never written down in the first place.
Almost every commercial cleaning relationship that goes badly goes badly for the same reason. The client assumed something was included, the cleaner assumed it was not, and there was nothing in writing to settle it. The fix is boring and completely effective: insist on a room-by-room written scope before anyone signs anything.
A real scope names the rooms and the tasks per room, and it names a frequency for each. 'Clean restrooms' is not a scope. 'Restrooms: fixtures disinfected, floors mopped, consumables restocked, nightly; partitions and tile detailed, weekly' is a scope. The second version is enforceable and the first one is an argument waiting to happen.
Confirm insurance before the first visit, not after an incident. Ask for a certificate of insurance naming your business, and ask whether the people actually entering your space are background-checked employees or day-labor subcontractors. Those are different risk profiles and you are entitled to know which one you are buying.
Ask who your point of contact is and what happens when something is missed. A serious commercial cleaner has a named supervisor, a defined response window, and a habit of correcting problems without a debate. If the answer to 'what happens if something is missed' is vague, that vagueness is what you will get at 6pm on a Friday.
Finally, look at how the price is structured. Fixed monthly pricing against a written scope is predictable and easy to budget. Hourly pricing with no defined scope means you are paying for time rather than for a result, and the two are not the same thing. We quote commercial work in the DMV on a fixed monthly basis for exactly that reason — you should know what you are getting and what it costs before the first crew ever walks in.