I just had a thought on this subject.
Now that the total distance for each city is part of the city entry, might there be some “completion metric” that compares “stride miles” to “city miles”? In @8f7162110d9eeaf907ab’s example (link), I suspect the Stride miles is going to be (much) less than actual city miles.
Perhaps in this case, a 
could appear next to the person, indicating something is fishy.
In most cases, if not all, Stride miles should always be more than city miles. In fact, I think at one time I posed (or maybe just thought) there should be a “city efficiency” metric. A number less than 1 would be the “something is y” metric, and the person with the smallest number greater one… Well you probably get the idea, but also will figure out this idea is not necessarily going to be accurate, as extra legitimate miles, can mask y miles. Note: a metric > 1, but very close to one, seems very unlikely.
I (kinda) say this in jest, because, while I really enjoy being the first person to complete several (admittedly smaller) cities in my area, my real satisfaction comes from knowing I got 
% in a city… In fact, I typically go back to 100% cities when/if I see (from my Lifemap) that I “missed” 100% of a street.
Update: Look what I found: Efficiency Score based on miles in a city & miles run