How can you be sure of this?
Basic physics, available as a simple mathematical formula. Electron repel each other, which means that they maximize their distance from each other in/on a conductive object. Add electrons to a human body and if the body is insulated from other conductors, the electrons will spread out over the surface. There is the electrostatic force pushing them away from the interior of the body.
low levels of Electric frequency
"Electric frequency" is a nonsense term. An alternating field can have a frequency, but you can't have a 'level of frequency'.
alter the frequency in which the cells operate on in their natural state?
Again, a term that doesn't have real meaning. Cells don't operate on 'frequencies'. They have electric fields and chemical imbalances, and flows of both electrons and ions. A cell might switch state at a certain rate of repetition over a certain period of time, which you could measure as a frequency, but that's like measuring the rate of raindrops striking a surface, and we don't normally talk about raindrops operating at a specific frequency.
The scammers marketing "earthing straps" and "healing frequency generators" and other such products rely on the poor level of scientific education in the general population. Words such as "electricity" and "frequencies" lack real meaning to a lot of people, and so marketers can easily mislead people with scientifically nonsensical claims. Someone might offer a mysterious gadget or "Himalayan rock salt crystal" that "emits healthful frequencies" and all too many people will not even think of asking the question "frequencies of what?" Frequencies have to be of something--alternating fields, goose flocks passing a point. Frequencies are just a numerical measurement of x/time period.
Likewise, when people don't have a good understanding of mathematics and physics, scammers can abuse that too. "Neurons have voltages measured in millivolts, while our meter shows volts from EMF!" The target is supposed to agree that the EMF field is 1000x bigger than the healthy neuron voltage, therefore it must be really harmful!!!!" However, as I pointed out, the reality is that regardless of the meter's reading on the outside of the human body, the voltage induced by the EM field is actually negligible across the parts of the cell where it might have an effect. The scammer might point to studies where voltage is applied across a cell, but leaves out the part about that being many orders of magnitude larger than what the cell would experience in a body near a cellular tower or wifi dongle or lamp cord.
What it boils down to is: don't take the claims of marketers as being fully honest. If you don't understand the science behind the claims, either learn the science yourself or base your decisions on people who do understand the science and who your trust to provide good advice. The more reliable experts you can get advice from, the better, since none are perfect.
