Red diesel on vehicles on the roads?

I had driven heavy trucks for years throughout north Jersey, TT's, roll offs, concrete mixers, etc. Only once was I ever stopped & checked, it happened at the exit of a stone quarry. I had never seen it before or since. Two guys in cop like uniforms with IRS insignias & a marked SUV waved me to stop, opened my tank and stuck a hollow clear glass tube to pull up fuel to look for color. They thanked me and I was on my way. I was driving for a huge corporation who would be the last ones to try such shenanigans, too. I would tend to think the little guys and small diesel vehicle owners would be the most likely ones to try to temp fate with running dyed fuel.

I know it's easy to do it if you wanted to, there are off road fuel pumps around here. Years ago I saw someone filling up his Mercedes diesel powered car at it, I don't know if he knew it or not, but now you can't self help due to newer pumps that need the attendants card to start them.