Charge more than cleaning, the product costs more, so charge more
With respect Paul I'm not sure that's logical
Yes, protector costs more per carpet than the chemical used to clean it, but all you have to do is stick it in a sprayer, apply and brush in! Time and equipment costs are minimal.
I don't think it's entirely logical to charge a % of cleaning price either... after all, as said above, cleaning costs vary a lot! If you charge cheap you might be paying the customer to apply protector to their carpet! Or if you charge high, cleaning plus protecting might add up to a silly amount.
I've played around with pricing protector a lot over the years, and have found it makes little difference whether it equates to an extra 30% or 60% on top of cleaning.. if the customer is set on having it they will pay the price, so you might as well make it worthwhile
I have a set amount per suite, or per ft²of carpet