I had always thought scarfed was a term and method only used in connection with bamboo rods. I had no idea that they have scarfed fiberglass rods.

I've done scarf joints on bamboo rods, both permanent and to tape sections of a rod together, and there's no way you could do this with a hollow fiberglass or graphite rod.

When a fiberglass or graphite rod section breaks, you can glue a smaller diameter rod section inside the broken parts to attach them. The old Shoff's store in Kent used to sell small sections of fiberglass intended for this purpose. I've never heard the term "scarf joint" used to describe this process, but it could be what the seller of the rod is referring to.