If you funded the original payment to the seller from your bank account or a card then once marked refunded/completed it will automatically go back to that bank account or card. Normally it can take a few days up to a week to go back to a bank account and a bit longer for a card, Paypal say allow 30 days for a card (1 billing cycle) but its rarely that long. (Can vary according to country though).
Advice is voluntary. Kudos / Solution appreciated.