Single engine Flight Instructor with trainee reported an NMAC while at cruise altitude.

Narrative

I was flying with a student pilot to do a tour of Location X. We were on flight following with ZZZ Approach. We were flying toward the Location Y bridge.I saw the offending aircraft on adsb-in; same altitude to our left converging. I immediately saw the silhouette. I don't remember the distance; maybe 2nm.I pointed him out to my student and I told him to get the aircraft in sight. I informed my student about right of way rules; and how the aircraft to the right is 'supposed to'/legally has the right of way according to 91.113(d). According to experiences I've had in the past; other airplanes usually never see me in the exact same situational circumstances and it's always me descending to avoid them. I told my student this as well; 'In this situation; we are 'supposed to' have the right of way; but I don't trust this guy to see and avoid us because of situations I've had in the past. They never see you and you can't trust them; which is why you need to always visually scan in VMC.'ZZZ approach then pointed him out to me as I told my student to descend to 2000'MSL to avoid him. I informed ATC I was vacating my altitude. The other aircraft did not see us; and if they did; they did not take corrective action to yield to us. If I did not give the order to descend aggressively (-1500fpm); we would have collided and likely died in my official judgement. As we were descending I then noticed the other Aircraft bank to the left slightly into our flight path. I then informed ATC controller he did everything right; and that it was the offending pilot's fault. ATC informed me the offending pilot was 'not talking to anybody.'I am the one who took the corrective action to have 500' vertical separation by the time he passed over us to avoid the official criteria constituting a near miss (2000' laterally; 500' vertically) despite having right of way. The other aircraft failed to 'see and avoid' and yield via right of way requirements.I would just like the pilot of this aircraft to be informed he needs to look outside more than he is; I don't want any licenses pulled because of this incident. It needs to be a learning experience. Keep the skies safe.