Generally the people who cheat in races and then get aggressively outed are the ones who stand to gain personally from their cheating. Usually the hobby jogger who bit off more than he could chew or who missed some training due to injury is left alone. The ones who are outed usually fall into one of six groups:
1) Boston qualifiers - cheating to get into the Boston marathon and so denying a legitimate qualifier a spot.
2) Business promoters - use their results to promote their fitness training business, the most recent is a Pilates instructor, or their online blogs etc. For example Gia Alvarez
3) Questionable charities - raising money for a foundation that is a sort of charity but could just as easily be going into their own pocket. See the Amy Hughes thread for a classic example of this.
4) Brand ambassadors - use their results to build up Facebook and twitter followers to get sponsorship from a fitness related company. Amy Hughes again
5) Stolen glory - cheat to get on the podium and gain prizes either overall or in their age group. Kip Litton would fit in here.
6) Serial cheaters - see the act of cheating to be the real challenge. How blatant can I be and still get the schmucks to not spot it. Kip Litton again, the article on him in the New Yorker is a must read.
If you are not in one of the above then probably nobody is going to bother you.
https://www.marathoninvestigation.com/2016/04/popular-blogger-banned-from-boston.html
http://www.letsrun.com/forum/flat_read.php?thread=8338355&page=105
https://www.newyorker.com/magazine/2012/08/06/marathon-man