A mechanic's log book of jobs is used when customers have work done on their vehicles and copies of invoices by the mechanic are kept for their records.
All the mechanic had to do was to refer to his records as proof of whether the job had been on the merc or not, as this is the normal procedure in a business transaction.
But I thought the job wasn't done, it was just an enquiry and the mechanic said he didn't do that sort of work. Would there have been a log of that?