I ran a test while on vacation. For the 3.5 weeks I was away, I changed the price of Emergency List from free to 99c to see how this would affect sales.
Before the price change, I had daily sales in the tens of units.
After the price change, I had three sales in 3.5 weeks. Zero sales every other day.
So I set the price back to zero two days ago, just to see what would happen. I did not in any way market the change. How would this affect sales?
I assumed that no one would notice.
I was wrong.
Lots of people noticed.
I had my largest sales day ever.
And yesterday was my second largest sales day (half the volume of the largest day).
How did they know?
For the record, I am not planning on making money from Emergency List, it was my first public iPhone app, it provides a simple and useful function, and it allows me to experiment and learn how to become a better indie developer.