Agents and Editors Aren’t Always Right About Market Potential | Jane Friedman

Some of the things that don't indicate market potential:

The opinion of your family or friends (unless they've done the market research themselves)
The opinion of the freelance editor you hired
The opinion of your beta readers or critique partners
The opinion of your colleagues

And finally, the one that frustrates everyone:

The opinion of literary agents and editors in traditional publishing-people who probably know something about market potential