Re: plug in earth products shouldn't be used in america or the uk?

Could be the result of corroded or loose connections along the ground path in the house, poor connection to whatever is the source of earth ground (grounding rod or metal pipes), poor conductivity of pipes (due to low iron content or slightly insulated threaded connections), or low conductivity in the soil due to lack of moisture or the soil itself.
The only true way to test your house is hammer your own copper grounding rod into the ground, connect your voltmeters negative probe to it (via another extension wire) and connect the voltmeters positive probe to the ground "hole" of your AC outlet. The higher the voltage reading, the worse your houses ground path is. Tweet