With ex lease cars, the lease company send of the red/trader bit of the log book usually and give you the rest to the buyer of the vehicle. If the person that had the comp car was a scatter brain and never handed the service book to the garage then it wouldn't be stamped. Both VW and the Lease comp should be able to verify this, so give them a call.

Its no big deal and not a crime if the person wants to try and top up their wages.

Personally I'd call the lease company and see if they have a similar car to the one you want for sale