GA pilot reported a near miss during cruise with an aircraft flying opposite direction at the incorrect VFR cruising altitude. Reporter took evasive action.

Narrative

While flying from ZZZ1 to ZZZ2 on Day 0 I was cruising at 3500 MSL. I had just transitioned through the ZZZ Class D when my ADS-B on my tablet alerted me of an approaching aircraft at the same altitude heading from my left to right (southwest direction of flight). I looked at the traffic alert and noted it was an aircraft traveling at approximately 170 KTS; and did not appear to be climbing or descending. I determined my best course of action would be to descend and did so at approximately 1;200 FPM; at the same time I made this decision ZZZ tower gave me a traffic alert. After being clear of the conflict I took a screen shot on my tablet of the tail number of the other aircraft; told the ZZZ tower I was okay; and noted that the other aircraft had climbed up to 4300 MSL (still not a correct VFR altitude for their direction of flight).I believe the pilot in Aircraft Y disregard for VFR cruising altitudes and improper right of way resolutions nearly caused a mid air collision. Without the technology and ATC I believe there would have been a mid-air collision between our planes; due to the other pilots dis-regard for regulations; or their ignorance of them.