old rego papers help,but get a receipt showing their name, address,licence no. then put all details of the beetle ie chasis no. ,engine no. and maybe old plate no. and have your details as well.. and to make sure its all above board do a revs check with the no.s etc that you have sighted and recorded yourself

http://www.revs.nsw.gov.au/ 

then if alls well you will have to book it into an auvis approved inspection station(blue slip) ,and when it has passed that you get your greenslip and go and get your rego