Although, in my opinion, selling open source software while contributing nothing themselves, is parasitic and unethical, it is not actually illegal to sell open source software. I would encourage any buyers to complain in the strongest possible terms to ebay about the deception.
Audacity could decide to change their open-source-usage-agreement to exclude any resale of o/source-software.
Without adjusting o/source-software-usage-agreements, such occasions will repeat themselves far more often.