If customers have good information (they are already using the app), and only one price (your IAP), or pricing you control (your IAP, with dummy prices - feature by feature unlocks, and maybe a premium feature or two), they'll spend be more likely to spend money.
The big money is in exploitive IAP. Skinner box games which use psychological tricks to goad big-spending "whales" (addicts) into spending more. But the small money is probably in IAP too - unlocking the demo.
There's no money (IMO) in $1 apps - they are too expensive (compared to free apps), and they sell themselves short.