my 2p worth….
I presume you bought the site and not the company – therefore you are not liable for the seller’s liablities. it would be treated as the same you buying a used computer from a company, you would not be expected then to pay for any of the company’s liablities.
of course if we were only talking about small money you’d probably honour their past deal/liability just to keep on the customer’s good side irrespective of who’s liable – but $5k is a different kettle of fish.
you shouldn’t have too much issue avoiding the seller’s past liablity but you’ve obviously been decieved.
Technically i’m sure you could sue him/her but is it realistic to bring it to court? i doubt so, i’m sorry to say – unless there’s some kind of chargeback you can perform on their bank