John at this moment in time i am charging +33% for protector
I use a very non pushy sales technique, when i give the quote i simply write the price with protector on the sheet and tell them that this is another service we offer but ask them not to make there minds up yet but to wait and see how the clean comes up.
I tell them basically not to commit as this stage but if the carpets come up better than they expected they would be mad not to have it, then all you gotta do is make sure you do a good job and if they are happy they will ask for it.
I also make a point of telling them its not bulletproof and its a help as opposed to a solution. I say to them imagine you have two sheets of paper and you laminate one, you can still rip it, mark it, burn it etc but one sheet will be a lot tougher than the other and you will be able to wipe things of the laminated one, this is what protector will do for your carpet.