But is there any harm in nabbing a pair of "Louboutins" from a market, or a "Chanel" handbag from a chap selling them on a foreign beach?

To the average punter it might sound a bit far-fetched but their cash goes straight to a drugs cartel or gun-runners.
Buying such items clearly poses a health risk. The same can be said for toys which aren't up to safety standards, and sunglasses which don't have the recommended UV protection.
But the vast majority of consumers know exactly what they're getting. The real issue is when people think they're getting the real thing and they're not. Those people need to be protected.