Ebay have some pretty funny ideas about what can and can't be listed occasionally, but under the Australian Telecommunications Act, only licensed amateurs are permitted by law to buy or possess radio transmitting equipment, and this includes linear amplifiers. Sellers need to sight the buyers current and valid amateur licence before selling said equipment and I suppose eBay figure that might be too hard to police.
You could try listing it on Gumtree, but as that is also owned by eBay, similar rules probably apply. Having said that, sometime ago now I sold my Kenwood TL-922 2kW linear on the Trading Post for $1800, no questions asked, which is $600 more than they cost brand new! People are still paying ridiculously high prices for them, even though they're old technology and expensive to maintain.
