I agree with Kung Pow Chicken (And also agree that it is delicious!). Derek might confirm, but it seems that RDs are more likely to DQ participants due to anomalous chip data compared with video or photo evidence (Unless there is proof of the individual jumping on a bike or in a car).
A cost effective method to prevent some cheating is to not publicize the location of timing mats prior to events. For similar courses run annually, changing mat locations yearly should occur. In cases where RDs prefer mats at milestone distances (5k, 10k, Half Marathon, etc.), the addition of 2 or 3 random timing mats across the marathon distance placed on race day would be recommended.
A missed random mat can be contributed to a technical glitch, in which case the onus should be placed on the participant to produce GPS evidence, preferably with cadence. 2020 LAM entry is $175. Adding on shoes ($50-$250) and clothing ($25-$100), the cost of a new Garmin Forerunner 25 ($86) should not be prohibitive in the emergency case where you must prove your results.
Unpublished and random mats do not prevent all cheating, but would help limit the type FM is alleged to have done. RDs would simply DQ participants who miss mats placed in unpublished locations, likely via automated means. It would be nice to have a ruling body that would hold all marathons accountable to such rules, so LAM doesn't act by different criteria for DQ than CIM.
Us runners know the pain, joy, and time it takes to train for and run a marathon. Emotions play a big role in this thread. Some people really care about the integrity of the race while others simply focus on the joy of running the race and not focussing on others, even in their age group (I envy those people in this case!).
Photo and video evidence convinced me that FM cheated and I'm looking forward to a major press outlet, like the L.A. Times, to give the issue professional coverage. I also (barely!) understand the current stance of the LAM not offering a DQ to FM as all mats were crossed with reasonable times. At this point, I want the issue to be public. It's a juicy enough story with sufficient evidence to go national and potentially force LAM to change their stance, offering a DQ.