From
http://www.flexcoin.com/?page_id=103Once the vendor accepts the transaction, the transfer would become final.
If it requires vendor approval, it's not a chargeback. It's a refund.
Chargebacks imply 3rd party arbiter with the power to reverse the transaction if vendor does not comply. That arbiter would be you.
If you are prepared to do this, lay down arbitration rules and make chargeback protection optional, I'm sure few people will object.