There is no such thing as a chargeback. It doesn't require rocket science either, and can be implemented, tested, and deployed entirely on self service basis. We will be implementing digital certificate based digital signature this summer for improved non-repudiation. Currently we rely on SSL protected Account number and password combo, same as OFX standard for banks. I thought, however, I might share an additional caution with you about what fraudsters can do with stolen or fraudulent credit card numbers.
Spammers evidently have a nasty habit of opening accounts fraudulently with fake or stolen numbers.
You correctly suggest being careful with free email accounts, and as a precaution asking for a pay email address. We provide Internet Scambusters as a public service and, unfortunately, don't have the manpower to answer the hundreds of emails we receive concerning your questions on individual scams, companies or chain emails. We've developed some excellent resources which you can use to find the answers you're looking for. And be sure to subscribe to Internet Scambusters to get the scoop on the latest Internet scams.