"If a transaction was reversed, what can I do?"
per http://help.dwolla.com/customer/portal/articles/99253-if-a-t...
What you can do:
You may request a copy of the affidavit from Dwolla, who will forward it to you. If you choose, you can then take further action directly with your customer who filed the dispute with the bank.
If you were intially the receiver of the payment, you may send a money request to the other party by logging into your Dwolla account. If you were intially the sender of the payment, you many send another payment to the other party by logging into your Dwolla account.
What you can do:
Contact the other party to work out a resolution.
What you can do:
Contact the Financial Institution directly to see if your account has been closed or is no longer valid.
What you can do:
Contact Dwolla to inquire about verifying information to ensure the account is reopened.
Links? Nothing obvious I am seeing even with a search for "how Dwolla combats fraud"
Additionally is there any difference (for a merchant) in how Dwolla handles chargebacks vs. a credit card company?