Or buying, for example, electric toothbrush heads at half the cost they are in the supermarket and then being surprised when they turn out to be counterfeit.

But that's the other aspect to commingling, I guess - you might pay full price for the real deal and get a fake, due to bad actors' stock being commingled, but on the flipside a punter who's paid an unrealistically low obviously-fake price might actually get the real deal, adding an air of legitimacy to the bad actor.