FBM order or FBA? The return probabilities will depend on the answer.
And “discretionary refund” means the buyer rang in about something so Amazon decided to give them a partial refund [from your funds off course] to compensate them for their troubles.

FBA

They have refunded them for the full amount, but how do we find out what for?

And do we actually get the product back since theyve been refunded…how do we know it wasnt something that happened to the product while it was with Amazon?

You can ask seller support for more info. They’re usually pretty forthcoming with the actual reason.

Once the item has actually arrived back with them then the reason can be seen in the returns section under reports > fulfilment by amazon. I’ve had it a couple of times but can’t remember the exact reason and when I found out the reasons it was OK. I think they were all delivery issues.

If the item doesn’t arrive back, you should get an automatic reimbursement.