How big does your audience need to be to advertise on the radio?
I listen to talk radio, mostly sports talk but some political and local, and I notice all the commercials for Zip Recruiter. Now Zip Recruiter isn't a job board (though they are starting to post jobs) but is for people hiring and they advertise all the time.
Now there are a couple other job hiring types on the radio.
There are other examples as well such as Grainger and Kronos. Those people only work with businesses and not the self employed type businesses but ones with employees.
There is very little info on marketing on the radio.
Does anyone know a rule for how large your audience needs to be to advertise on the radio?