hacked means?
he was not the owner of the domain?
or the domain followed the "domain hacK" model like dispir.in
if it is first case, you can surely go legal although the assurity of the money will depend on the proceedings
in the second case, was in your entire converstation, did you or the seller mentioned the domain name as "domainname.ext").
if it was mentioned, then case of forgery and cheating leading to financial loss and business productivity can be initiated.
and if it was not mentioned, then nothing much can be done to it unless he has a weak lawyer and you have a strong lawyer
---------- Post added at 12:22 PM ---------- Previous post was at 12:20 PM ----------
by domainname.ext i mean u thought of domainname.ext and he sold it as domainn.ame. If you mentioned domainname.ext in your conversation, you have a strong case with you. But follow up a bit more with the seller and simultaneously , start proceeding for legal action