Question is, where is the customer buying them from? If they are being sold in the UK, that's straight up illegal and the seller/importer can be prosecuted. If your customer is buying direct from China, that's much more difficult, and in fact your customer may technically be breaking the law by importing them. If there's a third party "sales platform" involved like Amazon Marketplace, Ebay, etc. you can expect a lot of buck-passing and denial of responsibility.
If I see an appliance with a plug/cable like that, I'm always inclined to question the safety of the rest of it. Only yesterday I refused to install a light fitting that a customer bought from China via Amazon because I could be found guilty of negligence for installing it, knowing that it doesn't meet UK safety standards. Admittedly in this case, it was very obvious that the thing was dangerous and even the customer could see why when I pointed it out.
Edit to add: I'd be particularly nervous about the hand dryers, as presumably they're being installed in public and/or workplace toilets? That could cause a whole heap of trouble if anything went wrong.