I have, years ago cleaned banks and building socs., but no more, thanks.
For security reasons, you need to use a portable inside the building and with all doors and window closed, it gets pretty hot and steamy - uncomfortable and slow drying.
The hours they want you to clean are inconvenient if you are a busy cleaner as they tend to want you there at 5.30, so you have to ensure that you leave an adiquate safety margin after the preceeding job incase of an over-run.
On top of this, most of these, I understand, are arrranged on a district basis and are very price-sensitive.
John.