It's not a military issue Bulgarian kit for sure.
Mil issue have:
- serialized gas tube (left side)
- engraved and painted trunnion serial (not dot-matrix, which is common on SLR)
- full auto carrier (the pictured carrier on GB is semi-auto)
- wood handguards (at least the one I have)
I would be cautious and ask the seller for pictures of the barrel crown and confirm that it's not a cut-down. The receiver section with the trigger holes does not appear to have the 3rd pin reinforcement. Also interesting that it includes a FA trigger, but no sear trip.
It's more likely that this is a demilled Arsenal commercial import SLR-104UR.