TPMS question

I understand from other threads that the sensors for Tire Pressure Monitoring System in the Prius are attached to the tire valve stems and rims, and that it's important to let the tire installer know about it.

Well, I just got back from Merchants Tire, and the guy I talked to said they replace all valve stems unless they are custom. But the Prius valve stems aren't custom - they came that way.

Do I

(1) try to explain (wondering all the while why, with all the Priuses around here, I should need to explain)
or
(2) try someplace else?

Also, if the owner's manual has any useful information about the TPMS sensors and just where they are with regard to the tires, I'd love to know on what page(s) that information appears. I have a feeling that I would be advised to take something in writing to Merchants before they believe me .... but at that point, will I be able to trust them?