Re: How?
"I'm assuming they require the owner to supply it which in itself should be a very large flag as in most cases (new battery, screen etc. ) just switching on should be sufficient to validate the repair. Sorry if the question seems to be a silly one but I am genuinely interested whether these repairers routinely seek the unlock code."
One of the strings to the bow of the company I work for is being an Apple dealer/authorised repair centre. Yes, the users access codes are required. Replacing a broken screen and simply confirming it works by turning it on is no substitute for doing a full diag of the system to make sure nothing else broke at the same time. If they refuse (some do) the warranty repair will be completed if possible and returned "as is" if only limited further diags are possible. The vast majority of what we deal with is corporate though, so in most cases a device, Apple or otherwise is either returned with a clean OS image or the customers specified OS image. All firmware is updated by default where applicable and all the hardware is checked so it goes back "as new" (in terms of functionality, case scratches ain't our problem), no unreported faults left unfound and unfixed unless, as above, the customer refuses required access codes or passwords.
And no, the guys in the workshop don't really have time to go rooting around in customers data. Diagnose, fix, test, onto the next one. Anyone caught doing anything untoward with customer data would be marched out of the door. Some of our customers are the type you occasionally see in the press as having left unsecured data on trains, so that's the sort of data that would be on some of the kit we fix. That sort of contract customer is too lucrative to risk.