While I can neither confirm nor debunk olivers answer, I might have some additional advice for you.
One of my clients is a tent operator in Stuttgart (where they have two annual beer festivals that are considered to be the runner-up behind Munich), and they are really very well aware of anyone selling tickets on public platforms, particularly "eBay Kleinanzeigen". I'm not sure how aware the Munich people are on this topic, but I can imagine they will also try to stop people from offering excess space there, particularly for excessive black-market prices.
However, you should check the terms and conditions of the tent, as at least the people from Stuttgart will usually allow you to sell the minimum consumption to someone else, as long as you charge exactly the original price to them. My clients have already canceled reservations from people who were trying to sell their reservation (or parts thereof) at double or triple the original price on eBay (sometimes even selling only the admission wristbands for as much as 60 EUR per person, without any vouchers!), and you surely don't want this to happen to you.
Under no circumstances whatsoever should you try to sell your remaining seats directly in front of the tent. This will almost inevitably lead to you being expelled from the tent (and maybe even the entire Oktoberfest area) without any refund.
I would say your best bet would be to offer your remaining tickets to anyone you might know across Europe, as, considering how difficult it actually is to get a reservation for Oktoberfest, they will probably jump at the opportunity.