I was at a customers the other day that had booked clean and protect , the carpet was trashed but for some reason she thought protector would help. I told her it was a waste of money (£50) I could have gone along with her misconception of what protectors actually do, but didn't, sadly many would have taken the money.
If you want to build a lasting relationship with your customers, it has to be built on trust and selling people products they neither need, nor in reality want, is one sure fire way breaking that bond of trust.
If a carpet comes clean after years of use, why would it need protector to make sure it does the same next time?
Upselling things like a second carpet cleaned half price, etc, gets you an extra sale and gives your customer a benefit they can see. The difference being that the customer thinks you've done her a favour cleaning something for half price, rather than a rip off merchant who sold them something that doesn't work, which they will find out in due course when it doesn't do what they thought it would do.
Having said that we do protect some carpets that are vulnerable to staining, light coloured, kids, pets etc, but only ever when i'm satisfied that the customer may gain some benefit.
Simon