The difference is public vs. non-public information. Doing something like counting cars in retailers parking lots is something any investor could do (or pay som

The difference is public vs. non-public information. Doing something like counting cars in retailers parking lots is something any investor could do (or pay someone else to do). Trading using trends from non-public credit card transaction data isn't something that any "general public" investor could do on their own. Also note this is about buying and selling securities, not selling consumer data for marketing purposes.