I would say that it is probably a pure T. s. elegans, unless the seller knew for sure that it was an intergrade and wasn't just guessing.
There's also a small chance that it is T. s. troosti, the Cumberland slider. They look much like red-ears but have orange ear stripes instead of red, broader light stripes on the underside of the throat, and smudgy, often hollow-centered spots on the plastron. I don't think they're very common in the pet trade.