"According to his study, in one day (May 9), playing one stock (Apple (AAPL)), Hendershott walked away with almost $377,000 in theoretical profits by picking of

"According to his study, in one day (May 9), playing one stock (Apple (AAPL)), Hendershott walked away with almost $377,000 in theoretical profits by picking off quotes on various exchanges that were fractions of a second out of date." This is a massive red flag. There's so many things that could be done incorrectly that the result is meaningless if the profits were only theoretical instead of observed.