I have the TPB return policy.

Download it when I'm interested what it's like. And delete it when/if I'm done.

A 24 hour/15 minute return policy is just an insult.

It'd probably be helpful if the store let the developer set the trial period. An appropriately set period is going to vary by what the software does and the devs/publisher are the most likely to have (a) the necessary insight involved and (b) the highest incentive to get it right.

I heard people would buy an app, "backed it up" with Titanium backup, get a refund and restore. Not sure if they put something into Android/Play now to counter that though...