I did radio advertising for many years. Much of it was trade out. Good rates when we paid cash.
We cleaned for two of the announcers homes (full price paid), plus the station itself. This allowed the announcers to throw in some personal comments about how pleased they were with the results they saw for themselves.
This worked great in a small town. One radio station in town. Only two in the entire county.
For a larger market, you will need to be sure you select a station where the listeners profile fits your target market. It doesn't matter how many people hear your ad if they aren't the ones who buy carpet cleaning.
It did take a while to build up.Very little response in the first two months, but after 6 months or so we regularly got calls from folks who were used to hearing us on the radio.
Scott Warrington