My experiences with “the other party“ have been nothing but positive. I do think that recent circumstances are probably at play here. I can vouch for the seller.
So per my understanding of registered HK receivers that remain in essentially Title I configuration (ie. 9x shelf, not a double PP) there is a non-serialized sear (catch) and/or trigger box that is married to the receiver, and the two cannot separate. With that in mind, does this have a converted semi trigger box with non-factory sear (catch) or a modified FA factory trigger box with factory sear (catch)? I would suspect the former.