When my best mate first opened the village garage he worked to very high standards and charged less than most (and still does), consequently he took a lot of business away from a nearby competitor.
Said compeitor attempted to spread rumours that my buddy wasn't doing all the work and wasn't replacing parts he was charging for.
My mate responded by offering customers all the old parts he'd had to replace back when the job was done and, because all operational parts of the garage are filmed H24 for security purposes, anyone can sit down and watch the full screen version of their vehicle being attended to.
It works a treat and the offer still stands.
If every pilot/flying organisation insisted on having all old parts returned, it would make life pretty awkward for the cowboys out there.
Additionally, if every engineering organisation was legally obliged to maintain a computerised link to the regulatory authorities which records a comprehensive report of parts used, where they were sourced and the actual work done, as well as giving a copy to the customer, that should clean up the industry.
I know that would take some organising and there would be a cost, but if it stops Julian's experience reoccurring or something worse happening, it would be worth it.