It is very important that everyone read the details of the Unity Asset Store EULA's policy for refunds and not be confused by the appearance of the 'refund banner' on product pages:
"All sales are final and there shall be no refunds except as expressly provided in this EULA or as required by law."
Refunds are possible, but only in finite cases. The Asset Store does not support a 'try before you buy' or 'take it back if you don't like it' philosophy. The EULA is straightforward on refund terms. Users may request a refund from us under the following circumstances.
It was purchased less than 2 weeks ago
Has not been downloaded
The asset does not work on the version of Unity that it is published for.
The asset contains illegal content. (never)
We're committed to publishing good products and your hands on experience with our products makes your feedback very valuable and appreciated! If you have actually run into a circumstance where the asset is effectively broken - please let us know!
In practice, the circumstances that we can issue a refund are quite narrow but you are always welcome to open a dialog with us via our support channels and we'll be happy to help in any way we can.