Sounds like someone lied on their site description
Once the transaction is closed you can dispute the listing through Flippa. If you're lucky they'll let you relist it free. If you've lied etc on your site description then the buyer may be found in favour and you'll have to pay to relist.
I recommend you contact everyone who bid on the auction and see if they can put in a good offer.
Well, if you provided wrong information in the listing, you got what you deserved. I would return your site also if I was in his shoes.
I guess you have no choice to return it, try to maybe get a new listing free ( IMO, don't think it will work) and learn from this experience.
I have been quite successful lately with my auctions, but I never used hype and always provided 100% real data. And never used "site is doing $xxxx/month if it only reached that number one month.