Which payment processors support refunding payments from within CiviCRM?
I know it's not helpful for figuring out who did it in the past, but in-app refunds is a feature that Alice has written for TSYS that we'll be including in the next major version.  There is some coordination that needs to happen on how CiviCRM treats refunds, because if the payment hasn't settled, you're really voiding it rather than refunding it.  CiviCRM doesn't distinguish the two, so we want to be sure that reconciliation isn't a mess.