According to a
brief that PBusardo has on his website,
"Retail staff can instruct and demonstrate how a device is assembled or a tank is filled or how eliquid is dripped. They can not assemble products for customers. That would qualify them as a manufacturer. To that point, repairing or adjusting a customer's device is also considered manufacturing."
One of my buddies who works in a vape shop in Ohio had this customer come into his shop today, who needed a new coil made for his setup. As you can see he is physically challenged and can't make one for himself, and no shop employee could help him according to the FDA. Luckily another customer was kind enough to help the dude out.