[AI2V]

Finding a house that has it's polarity mis-wired is not common. If you question your house wiring, you can measure the AC from the smaller outlet hole to the center cover screw or a radiator or some other known ground; or you could buy one of those cheap yellow socket testers and be guaranteed of proper wiring.

In all radios that I own or have serviced I use a polarized plug with the smaller prong (line) going to the switch. I also disconnect any capacitor that is connected to this line side but always leave the neutral side with a cap.

The difference in reception will probably not be detected; there is an awful lot of capacitance in the wiring and whatever RF signal that is on the line side will be coupled into the neutral side. This capacitance will NOT be in pre-1930 houses with knob-and-tube wiring; even so, I have never found a difference in reception.