When I went to a local Apple Store to replace the battery of my iPhone 6, they asked me to disable Find My iPhone and explicitly told me to do a factory reset. I thought that was a good standard procedure, as I already did a reset though didn't disable Find My iPhone.

On the other hand, when I went to repair the keyboard for my MacBook Pro, they did ask for my password. I refused, and they just said they would have to wipe the hard drive and do a reset.

I guess it really depends on how responsible the individual "Apple Genius" is.