> They have file extensions turned off, which is the default, so they probably don't even know what a CSV is
And if, also by default, Excel is setup with an association with CSVs, the CSV file will, in addition to not having an extension to identify it, will have an icon which identifies it with Excel.
1. They see a file (they have file extensions turned off, which is the default, so they probably don't even know what a CSV is)
2. They double click it
Excel now corrupted the data. That is the problem. Good luck teaching all end-users how to use Excel properly.