Spots are sold based on one of two things:
In non-ratings based transactions, the rate is based on an advertiser's perception of value, the relationship with the seller and the ringing of the cash register. In ratings-based sales, the rate is based on audience delivery where a station with twice the audience generally can get about twice the rate as one with lower audience.
A station with low ratings or which does not get great results for clients might be filled with cheap spots, while a more listened to station has fewer but more expensive spots.
In Bend, KXIX is about 8th in total billing. KSJJ bills twice as much and has more than twice the ratings. So you can see the relationship.
Major advertisers will use multiple stations in a campaign, as each station only reaches one segment of the population based on format, age, taste, etc.Also, are there spots that are sold to every station in a particular market at different rates? It seems like 90% of the spots on the radio in my market are the same on all stations. KOMO and KRWM have some of the same spots that KPLZ and the other CHRs don't have, and there are some spots that only appear on certain stations, but again, most spots are the same. Is this usual?
In a market like Seattle, an agency buy for a big account might include 10 or more stations. Agencies use a calculation called reach and frequency to select stations that complement each other by adding additional cume and achieve the right number of average weekly impressions to the campaign. Agencies specify a goal as to rate against their target audience and stations that contribute to the campaign's effectiveness are bought if they meet the rate goal.