Hi,
What people would need is a photo of the selvages, I believe, to see whether they are original.
I actually think the rug looks nice, the tertiary elements (the playful little motives) are not entirely symmetrical, which shows the weaver took a certain creative liberty, which is often missing in semi-antique rugs. And if you have the rug not as an investment, but for your enjoyment, it shouldn't matter whether it is complete.
As to the seller, the rug a bit looks like those from Pakobel. They have the habit of using parts of rugs and rebinding them or even putting a border from a different rug around them, and they call all those rugs semi-antique shirazi, whether they are shirazi or not.
Equally, they sell rug fragment-patchworks where lesser worn borders of worn rugs have been sown together, sometimes with extra guard borders added on two or four sides, and they call these semi-antique baloch, although the weavings are mostly not balouchi weavings.
I personally don't mind this: you can usually see the patchwork well on the photos, and it is an interesting way of recycling used rugs. You still get the benefit of the hand-knotted look, even if part of a patchwork rug. (Yours is not patchwork.)
