I have been dropping off bids and talking to customers about roof cleaning work and sometimes a customer will say that they received a bid for roof cleaning where the other company is going to treat the roof only. It is usually for a ridiculous amount of money. Customers and home owners beware, this is a way of riping you off and stealing your money. This method absolutely does not work, there is no such thing as magic. The moss will turn brown and look uglier then before, and it will come back to life in about 6 months. Moss has to be removed, safely and effectively. Treated before or after the removal process. If the company wants to treat the roof in years to come after the moss is gone to ensure that it will not grow back then that is absolutely fine and the is the best thing for the roof.