I agree that the course should be 5k if advertised as 5k. That being said, if the course is not advertised as certified, then you should not expect it to be accurate. As mentioned earlier, if you want to test yourself over a "true" road 5k, find an historically competitive certified 5k that is operated by a RD with a solid reputation.
If it is a new race on a course that is not certified, refer to the "You Know You're at a Local Fun Run When...." thread for further guidance.
I am not too big on comparing times from one road race to another, so I don't see why everything has to be a 5k or 10k. I would prefer if more races were for odd distances, similar to Falmouth, Manchester, etc.
If it is a 2.85 miles loop from the firehouse, around Smallville and back again, then that should be the race distance for the Smallville Pie Run. There is no need to throw in a loop around the Elk's Lodge parking lot to try to make it a 5k.
If more courses were designed that way, nobody feels that they were short changed or lied to. Your time is only comparable to other people in that race and to the Pie Run legends of days gone by. There is no desire to compare it to your time for the Springfield Dog Shelter 3.3 Miler.