I use Steve's questions. When you say "re-apply", that opens up questions.
Then Education! Thats where Jim's sheet comes in, and the brochures if the protector you're using has them. Dupont, Maxim, SG I believe all have a brochure to explain the product.
I don't push, I offer. And I tell them about a personal experience I had with it where my daughter spilled a glass of milk. I didn't run for a towel, I just stood there looking at it for a minute at how it was beaded up on the carpet!