So moving charged particles in vacuum produce photons on their own. How do we know there are photons produced and not something else with right energy that happ

So moving charged particles in vacuum produce photons on their own. How do we know there are photons produced and not something else with right energy that happens to act on our sensor? Specifically, the sensors that use photoelectric effect do not react in the right wavelength, while standard radio sensors are also sensitive to charged particles. And presumably also use this exciton/pi-tons interface. How can we exclude it? Presumably fire photons from putative EM field at neutrons, observe emitted photons with wavelength change? (Essentially Compton scattering experiment with neutral particles.) My whole problem here is there's a lot of "seems as though" in those experiments... Like when you try to measure center of charge with it.