Friendly Flasher to a Shotgun in the Back during Trails!

I was in the middle of a trials run in Spaceport (Electromagnetic Storm). I was in what I thought was a friend lobby due to interactions with others before incident (+ im 100% PVE and now signed up for 3rd expedition). Anyway, half way though my run, I see a raider in distress being cornered and stuck surrounded by fireballs. I announce on mic im friendly, do the universal a million flashes, and also do a 'Dont Shoot' emote. He also flashes a few times back too, but no mic. So I help him and kill all the fireballs. I even dropped a BP and a Gold Boat as I found then during the trials run and dont need them. I let him know I've dropped them, flash on them for him to pick up and say I'm doing trials and found these, but dont need them. He then flashes me a few time picks up items then walk behind me out of my sight an 20 seconds later vulcanos me in the back. I say on mic again I'm doing trials and that I even came to help him as I saw he was in trouble. He just kept shooting until I was back in Spain. So, I added him on PS and sent message to say not cool to flash and do that. I said fight, kill others etc, but dont pretend flash and then shoot someone in the back. His response "Do you know how many times I've been killed like this. I was also friendly until I started getting killed all the time. So I do it now. I blink and then do the same, its better, dont trust anyone" (I think he's not 1st language English, possibly German) So in conclusion, this guy, because he's poor at the game and was getting killed all the time now purposely flashes people to gain their trust and then shoots them in the back. A real piece of 💩 - Raiders please continuously find him and repeatedly 💀