First of don't go in all guns blazing, you may well remove the coffee PLUS what ever they would have undoubtedly used to attempt removal, with just a good old fashioned high temp clean, then ramp it up if need be as you go along.Carpet tiles are pretty resilient and the ones that do not clean up so well just lift up and place under units etc where they can not be seen so clearly, using the clean ones in their place.obviously make the client aware of this.After cleaning go round with your bonnets to speed the drying.
If this fails I doubt you will remove the coffee stains etc with just bonnet cleaning you could be wasting a great deal of time and have a potential decent client feel let down.Just be honest with them over results with LM cleaning if they insist on this and drying times if you hit it with HWE.