If they were caught it would make headlines, the stuff's probably already been pawned off by now.
Yep, it's probably a good idea to ask for a receipt or something of the sort if you try to buy a newer Mac off of craigslist. Obviously it wouldn't work for the fancier stores like the NY 5th Ave location, but I'm surprised they don't just use a gate of some sort like:

I suppose it doesn't go with the "Apple aesthetic".