Flooding basement - what do you know about French Drains?

[Mindy Jensen]

My neighbor's basement is flooding after some pretty heavy rain over the past week. They have called a basement guy out, who would solve the problem by jackhammering up the cement floor in the basement, digging a trench and installing a French Drain that goes into a sump. Has anyone done this before? Did you have success? Do you know the benefits of interior vs. exterior french drains?

Thanks so much.