I've timed/worked at a few races where there are multiple events/distances that all start at the same time. And it has happened more than once that participants have gotten misdirected - completely off of course - or misdirected to the incorrect course.
One young lady was disappointed that she got told to go to the 10K, even though she was supposed to be running a 5K, she told me she should have known because she saw a sign that said 5K in the other direction, but she was listening to the course volunteers. She realized she should have gone with her first instinct, but then she was ecstatic when I told her her time...her pace was lower than what she was aiming for on the 5K on the 10K! (My husband might say that indicates over training...)
One of the things that surprised me, as I was looking over USA Triathlon rules, is that the participant is responsible for knowing the course. I have mixed feelings about this. On one hand I say "yeah!" it's not the Race Director's responsibility...and on the other hand I say...That might be quite difficult being a participant - how would you familiarize yourself with the course, so much so - that in the "heat" of the race - you are following the correct path.
Along the same lines...I don't know how many times I've been asked, "Is the course well marked??" This question gets me every time...because I wonder - how in the world does this person think I know?!?!? Does he/she think that prior to the event - at say 5 am - all of the course workers run the course?? Or maybe he/she thinks that I personally marked the course...and even if that were the case (which it isn't most likely) - what is their definition on "well"?? Do they need a reminder every 100 feet, yards, every mile, every 5?!!? And what if it is marked every 100 feet, but it's a tiny orange sticker that most people won't be able to see?? Or maybe...just maybe...the person who marked the course used invisible paint...or what about bread crumbs? Everyone knows bread crumbs are a good way to mark their path...(Ok, so that is just my cynicism speaking...)
Unfortunately for the participant, I tell them honestly. "Unfortunately, I don't really know." Sometimes I even add, "But I assume so." But you know what happens when I assume?? I make an a-s-s out of "u". (...and me...)
ETA (Edited to add): I am not trying to bad mouth participants or certain race directors...I know these things happen! I just wish they didn't for both sides of the race!!