For example, in The New Yorker, James Surowiecki reports that a 2012 study by Anita Elberse and Jeroen Verleun found that those endorsements increased sales by 4%. Later achievements will jack that up even further.
The play book on that goes way back to at least 1934. That's when the cereal Wheaties featured athletes on its boxes.
There are two recent developments, though.
One is that social media and social networks expand their reach. Likes and positive comments allow consumers to interact with the promotion. Sharing can multiple page views exponentially.
Contracts could only be for a year. That protects marketers from myriad kinds of risks. Suppose the athlete goes into a slump.
Also, as with the situation with Ryan Lochte, termination of contracts can be immediate.
Speedo was among the sponsors which dumped Lochte pronto. They could do that legally because of the morals clause in the contract gave them the exit ramp. And they are taking it.