research the vin number/rego plate online.... reg office, insurers, compliancing... if somethings wrong you might find it that way.
i think 120000km is a bit high for the year, but that might be the only reason for the price
*edit* start here, it will tell you a fair bit (click on highlighted blue things for more details)
http://raws.infrastructure.gov.au/rawswebpublic/RAWPubVehSearch.asp