Plumbers (reputable ones, anyway) are generally bonded and insured so that customers know they will do what they say they will do without causing undue damage (see https://www.angieslist.com/articles/hiring-contractor-whats-...).

Does Apple provide any insurance to protect/reimburse the customer if a Genius misuses their access to the customer's device?

The plumber analogy is a bit silly, as it is not access to the hardware of your phone that the author is objecting to (which would be analogous to your home), its the confidential private information that is stored on it. The issue is not that you think the Apple store employee will steal the 128G of flash memory from the hardware of your phone, it is that he will copy credit card or other personal information from your phone. The assumption here is that having access to an unlocked phone gives access to these things.

Yes people do give service professionals access to there homes, but unless they are hopelessly naive they don't leave credit cards, money, jewellery and guns around.

If you read the fine print in the agreements you make to have such items you explicitly agree not to allow other people access to them.

The scary thing is that responses here don't seem to be playing the devils advocate and actually seem to be believing this is OK.