Noticed a similar thing earlier this year, while I was crossing the border from a non-Schengen area country into the Schengen territory. The owner of a new Audi Q5 or Q7 just in front of me received all sorts of questions from the customs guards, while me and my gf passed the border in a breeze. We were driving our 12-year old small 1.4 liter hatchback, which has scratches on all its four corners, I said to myself that were we to transport anything illegal nobody would have suspected us.

While it is difficult to catch everyone at a border within the EU I would believe that there is a subset of border cops that can sniff out smugglers. Since you didn't smuggle anything they were correct in not suspecting you.

I know that. But as the OP said, it’s interesting to think about an anti-anti-smuggling technique like the one where you’re using an hipsterish couple to physically carry things for you, instead of some tattooed guys.

Registration plates matter a lot too. If you are from certain countries, you'd be checked much more often.

smart. Assuming there's one unit in the road, they'll be busy checking the pimped-out ride :)