[stetrain]

App stores could offer free trials for paid-up-front apps, or generous refund windows.

As far as I know the major ones don't offer this, Apple for sure doesn't. I think the store runners would much rather see developers use subscription pricing that gives them a recurring cut as well.

[baxtr]

Apple has refunded me every single app that I purchased accidentally. Every single one. No questions asked.

[i5-2520M]

Play Store has a no questions asked refund window, but it is very small.