Earlier this summer I ran a local 10k, which also has a 5k that runs simultaneously on overlapping parts of the same course. Volunteers were standing at various corners, with signs with arrows. At some corners, it was "left for 5k, right for 10k" or whatever.
A small group of us was at the front of the race and a volunteer waved us to the right -- she had no sign. We get about a half mile further on and someone notices that we'd already been there. We kept running and, since no one knew the neighborhood well, kept following the signs. We ended up looping 2.5 miles back around. (In retrospect, we should have turned back at that half mile point.)
Eventually we got back to the corner where we'd turned right. Now there was a second volunteer there, and both volunteers had signs. "Left for 10k."
So yeah, a 9 mile 10k and we all decided, as we headed toward the finish, to take a DNF and ask for a refund. Which we received. I don't understand the posts about not asking for a refund. If they screwed up your race, they owe it to you.