I can't believe people are pro 2A in other threads but fine with virtue signaling in this one.
The OP was selling a rifle to someone he doesn't know, got an erie feeling because some other guy was there, and decided against the sale. I regularly bring friends with me that know better than I do to purchase expensive items. You have absolutely no evidence that it was a straw purchase. For this type of sale, a straw purchase isn't necessary anyway.
If you're paranoid I suggest you sell the rifle to someone you know or via a legitimate referral. Better yet, put it on consignment and pay the commission for peace of mind.
I suspect that we have more to the story because none of this adds up. Especially after they allegedly kicked your car.
I don't understand what you mean by "virtue signaling" in this particular context.