My view on this is that many people don't consciously think about the size of the window cleaning company they are using. They want their windows cleaned for a price they agree is reasonable to a standard they accept, at an agreed frequency. Trust is important, but it begins with the initial contract made between customer and service provider, be it verbally or in writing.
If all criteria are met and maintained, the business relationship will continue. If any are broken, then it will be at risk. Whether it's a sole trader or a national conglomerate, it's irrelevant imho.
John