The number of custies who when cleaning their carpet said they 'had it Scotchguarded, but I don't think he did it because liquids don't rest on the surface and it get dirty'
When I clean it I know it has and on several occasions stuck up for the previous cleaner. The last one the custy informed me was dead at age 47 (as if he deserved it or something)
Anyway the only thing CC who sell protector are guilty of is setting up false expectations.
When I know it would be good for that customer's set of circumsatnces (which is a lot of the time) I sell it hard and that means explaining limitations too. The key is, once 100% sold, to take it away, tell them you don't want them to have it unless they are convinced it's right for them.
Tell them they have to weigh it up themselves, it will still get dirty, it won't necesarily 'bubble' liquids etc etc.
9/10 they are even more up for it but you won't ever get buyers remorse
I evaluate fibre type, pets, kids, traffic, how long they will keep carpet, carpet quality/cost, location ie hall-bedroon, middle class red wine alchies etc. to decide whether to advise protector.l
I NEVER consider whether I think they can afford it or not.
Mike