its a bit wierd why the police wont help you
we used to get police reports (at my old job) usually one every fortnight ish for some ebay auction related
the victim would contact cops and say xyz on ebay sold me stuff and ripped me off
police would file police report and contact ebay and say give us the IP address for user xyz
the police would then find the netblock owner for the IP address and contact the ISP
and ask for subscriber information for IP address @ date/time and the ISP would give up the details
the police would then have the home address , full details , credit card etc of the ebay user
this would require a full report and search warrant for the information etc