If the party is too clueless to set up the GPS right, then they're quite likely to be clueless regarding terrain association and general landnav awareness. I have had people as diverse and supposedly knowledgable as pilots and SAR techs not be able to explain to me what the difference is between NAD27 and WGS84 datums. I've asked said personnel "what datum do you use with your GPS system?" and the answer was "decimal degrees". Further prodding did not yield anything close to the correct answer.

You can dream up all kinds of accumulated errors to be made with the GPS. But if that's the case, the people are also not going to be able to get all Lewis & Clark with they're big bad selves and be geniuses with map, compass, and terrain association.

The GPS is a fantastic tool in the hands of a capable user. Don't blame the horse for the rider's failure.