From previous experience, you should have no problem getting a refund. I got scammed for $49 for an ebook that I never recieved. Took two weeks but got my money back.
Buying AdWords vouchers is the same as saying "I don't need this money!" - you need to be very careful when doing such a deal ! By the first - ask him for a test voucher, and check if it works or not. Second thing - never buy 5 or more vouchers at the time .. split your deal into smaller chunks
A lot of people got scammed by the vouchers recently especially those wanted payment method as moneybookers. Maybe that tell us something.
I appreciate your concern, but I'm not going to sit here and let you tell me what my experience has been based on the reputation you've read about and your experience. Hopefully you understand. No they do not. I've had to file a dispute for nearly the exact same situation twice where the only differences were 1) The domain name involved 2) The other person involved besides me I was the buyer both times, I lost the dispute that happened when my Paypal account was still relatively new, and won the dispute where my account was the more mature account. You're free to believe whatever you want, but experience and logic tells me that they side with the account more likely not to be a problem later.
Perhaps, I have heard for the 1st time, PayPal favoring a seller. And I am sure you were a victim of a well planned and organized crime where the sellers had made their side clear from all sides. BTW, I will appreciate if you can narrate your story in depth. I not able to understand the domain, the other person. May be I can figure out what could have happened.