Inverse polarization of appliances
Appliances are supposed to be approved by a competent testing agency.  This might be TUV or CSA, and the EU has a scheme where EU manufacturers can self-certify.  

Part of the certification is confirming that the appliance is insulated sufficiently for reverse polarization, assuming it comes with a plug capable of being plugged in backwards. (A non-issue on UK and US plugs which are polarized). 

This, however, is only as good as the testing agency.  This is where the sea of cheap foreign junk enters the picture.  A lot of mail ordered items bypass product safety laws and customs, and have never seen the inside of a testing lab.  For those items, your concerns are very much warranted.