There is a big difference in selling a "turn-key business" and a window cleaning round.
Those that have organised their business with automated systems for advertising, book-keeping, collecting, training of staff and then are willing to have a hand over period where they train the new owners in all the sytems and introduce them to all of the customers are sitting on a very valuable assett.
But they would need to be just as proffessional at marketing their business to maximise that value.