We are all built differently. I had a runner do that in a race in downtown Detroit years ago. I started out conservatively the first mile but after that point, only one runner passed me and he was running it easy (olympic qualifier). I said hi and could not keep pace with him, but NO ONE passed me from the mile on. When I finished, a runner asked me how I did and I said 32:50 something. He then said this is what I ran, and he showed me his watch which was faster than me. I said flat out, no way dude, no one passed me but Don. I said I passed you before the mile mark and you never passed me again. His face changed colors and he said then why does my watch have this time on it? I said because you stopped it before you finished or you ran a different route. His faced changed about 3 shades and he just walked away, never saying one more word.
Sorry, I worked too hard and money or not, I will call you out if you cheat. If I were a RD, lookout. I'd have people along the way with cameras set up, and I would not make it well known.